I have 105 zigbee devices attached to my C-8. using channel 25. I have no complaints. When I first got the migration done from C-5 to C-8 there were some strange things happening. Including dropping off the mesh. However, the devices came back by themselves a few hours later. Been very happy so far.
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Thinks were wonky with c8 (in terms of dropoffs) till i got sonoff 3.0. Dongles which makes sense from reading above... however initial joins can still be a whore/chore.
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Thanks for the descriptive post! Makes a lot of sense as to what's going on in the background. I believe this is what is happening in my situation.
I personally would love the option to reduce security to see if it solves my problems, even as a temporary test.
Still no luck getting my Ikea blinds to pair. I even took one of them down and brought it into the same room as the hub and tried pairing. Similar issue as before, where it finds a Zigbee device but doesn't get past the initializing stage.
Zigbee is currently on channel 20, and my WIFI is on channel 11. Channel 11 is optimal in my location with other WIFI networks nearby. Though looking at the channel graphs there might be some channel overlap causing issues. I have 2 AP's, one is maybe 10-12 feet from the hub, through a wall though. I think my next step is to play with WIFI/Zigbee channels to see if that will help my performance at all. Think I am going to switch Zigbee to channel 25, and let it sit for a few days. If that doesn't seem to make much of a difference I will swap my wifi channel to 1 or 6, and see if that helps. Hopefully things work out, but time will tell
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For reference, do you know what channel your WIFI is set to?
Well positive update, but still monitoring things. I did some more WIFI analysis, and ended up switching my WIFI channels to 1 for my home networks. Seems to be a lot of traffic on channel 1, but most of it had really low signal strength, so I'm not too worried about interference. Having 2 AP's definitely helps with range and signal issues as well, from a WIFI standpoint.
Kept my Zigbee channel on 20, with power still set to 20. Things seem to be responding well, and the outlets I was having problems with are all connected and responding. They all came on today when they were supposed to, which is the first time recently they are all behaving.
I did add a mmWave sensor to the mix today, and didn't have any issues pairing it in the same room as the hub. Moved it a few rooms over, and it seems to be working nicely.
Still haven't messed with the Ikea blinds today, going to wait a little more before I do that. Also, its just been me home today, so having a few less WIFI devices here is probably a nice bonus.
If all stays cooperating, I'll probably start dialing back the Zigbee power level, as to reduce strain on the Hub's radio. So far, pretty happy, but I'm going to keep monitoring to see if it keeps up
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When you get to that, if everything else fails, try keeping the blinds (the end where the battery is) really close to the hub, to make sure they pick the hub as their parent (and not any other zigbee router).
I don't have the blinds, but this procedure is required to pair the other battery-powered IKEA devices (buttons).
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Thanks for the tip. In the meantime I repaired the Ikea buttons to the blinds so I can use them without walking up to each one and hitting the up or down button (I know how terrible). In their instructions they mentioned holding the button really close to get them to pair. I'll probably pull them all down and pair them right next to the hub and see if I can get it working again. Might try it tomorrow, if everything else is maintaining.
What I find most stable for most people is 6 and under for wifi, 25 and above for zigbee with 12 for power. For myself and helping others, it seems to cure 99% of the issues...(caveat... issues that don't involve aqara, xiaomi, and sonoff)
@Tony
Thanks for that very clear and insightful description of Zigbee 3.0.
Is that the reason for the pairing option "avoid Zigbee 3.0 repeaters"? '
And, is that how they do it? (speculative, of course.)
Thanks, WIFI is currently on channel 1, but Zigbee is still on 20. Thinking I am going to need to try changing Zigbee to channel 25 to see if that helps. Saturday and Sunday, everything performed pretty well, but yesterday (Monday) I noticed the two older Sengled outlets (E1C-NB6) I have been having issues with are still acting up.
I was able to get an Ikea repeater plug to pair, and stuck that in the room with the two problem devices. Going to try to get them back online today at some point and maybe since the repeater is there they will start cooperating a little better. For whatever reason that room seems like sort of a dead zone for these plugs. Its funny though, because I have two of the newer Sengled plugs (E1C-NB7) in the same room, and they both are perfectly fine. I have 4 total of the older style Sengled (E1C-NB6), and the two that are in different locations are totally fine, but the two in this room aren't.
Honestly, since you mention Aqara, it might be related to these devices. I have 5 temp & humidity sensors, and 2 contact sensors (all battery devices). I noticed a couple had fallen off and re-paired them Sunday evening. Seems like once I did that then the other things began acting up again. Previously things seemed to play pretty well with the Aqara devices, aside from them randomly dropping off mesh and needing to be reconnected.
Any thoughts what might be best to try next? Remove Aqara, try channel 25, pull the old Sengled outlets and light them on fire? 
I do like the older Sengled ones because they aren't repeaters. I have been using them for holiday lighting and temp test switches mostly. So if they get pulled and thrown in a drawer for a little while in the past it really hasn't bothered my mesh. Though it seems the Zigbee gods are punishing me for it, because I know this isn't the best practice 
Non-repeating Zigbee devices should not be impacting your mesh unless they are bombarding it w/excessive activity and/or have a very noisey driver, which I doubt they are/do.
Aqara devices in general are unlikely to hurt your mesh more than any other device, unless similar issues w/noisey drivers that are generating excessive traffic or errors due to calls to deprecated features. I run Aqara on my C7 & C8 and do not have issues w/them causing problems. On my C8 they have actually been more reliable than Iris v2 motions and Visonic contacts.
I'm mostly using this one for my Aqara contacts.
What settled my C8 down the most seems to be repeaters taking the load off the hub...in recent testing I've determined that pretty much all of my Zigbee battery devices on my C8 are routing through repeaters rather than directly connected to the hub. My best repeaters are SonOff USB dongles, Tuya USB repeaters (the tiny ones), Iris plugs, & Ikea plugs. C8 power is set to 8.
During the time when devices were repeatedly failing to stay connectd on my C8 (and oddly, this was led by usually very solid Samsung/Centralite leak sensors, Iris v2/v3 motion sensors, and Visonic contacts) I moved those devices back to my C7 and hub meshed them back to the C8. That seemed to be the other key part of things settling down and I've been running pretty much issue-free since then. ~90 Zigbee on C8, ~35 Zigbee on C7. Stock Zibee antenna on the C8.
I did do an antenna mod for Z-Wave on the C8 - it sorted some issues I'd had forever on the C7 and to less extent on the C8 w/some Z-Wave iBlinds that had trouble communicating once in a while to the hub. The antenna (Bingfu 4G LTE RP SMA Cellular Antenna 7dBi Outdoor Antenna) provided solid connectivity (the iBlinds are communicating through the metal housing of my blinds) and they have been perfect since.
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I'm not sure how this option would be able to address the link key issue (or even if it was intended to). Zigbee uses a 'trust center'-- a logical entity responsible for distributing security keys. Zigbee doesn't require the TC to reside in the coordinator, but that's the way it works in Hubitat's implementation: any router intercepting a join request acts as intermediary and passes requests for keys to the trust center so (in a Hubitat mesh) all security key distribution is handled by the hub.
That being the case, I don't know how avoiding Zigbee 3.0 repeaters during pairing would make it easier for legacy devices to join.
AFAIK , a joining end device simply responds to one of several broadcast 'beacons' from any router in range that has child capacity to accept the join. I don't know (there's a LOT I don't know) how a joining device could distinguish a 3.0 repeater's beacon; maybe that distinction is made at the hub when the key request gets passed to the trust center (I assume that the hub can distinguish the protocol version of any router that it is communicating with; maybe the hub selectively issues a 'network leave' request if the joining device's link is via 3.0 repeater).
It's a mystery... just like 'network rebuild'. I can see that function's affect on the hub's child table (it seems to purge it of entries that don't exist anymore) but whether or not it has any affect at all on the rest of the mesh is unclear (my uninformed guess is that it doesn't).
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Thanks for the Aqara notes! I've been following your progress with Zigbee instability for a little while now. Your stability of bringing the C7 back and using both hubs made me think about doing the same, but I wanted to try and see if I can get things to cooperate a little better before taking the more drastic approach of running two hubs.
I've been using this driver for the contact sensors, this driver for temp sensors, and this for my leak sensor. Forgot to mention I have an Aqara leak sensor too. The devices keep piling up, I forgot what I have around the house
Researching in the thread you linked with Aqara driver recommendations, someone mentioned the drivers by Marcus could be problematic. Turns out I have my contact sensors running those drivers, I recognize the warn logs from the screenshots.
Was able to get all the contact, temp, and leak sensors swapped over to the chirpy driver, and they seem to be responding well initially. I did initially swap to the 'device' driver, clear all states/schedules/etc, and then swapped to the new driver. Some of the temp sensors liked dropping off after a while, so hopefully the driver change will help with that. Fortunately, they don't do much other than log temps for reference, so no real harm if they do drop off.
As for the older Sengled plugs, I am thinking I might have to replace them with different devices. Early this evening, the two cooperating ones turned on when intended. Though after some testing tonight, neither wanted to turn off when triggered from a dashboard or the webpage. The two problematic ones I cannot get to 'pair in place' where they are located. I can only get them to pair when they are in the same room as the hub (I have been pairing them within feet of it). I have 6 of the newer Sengled NB7 sitting in boxes that I picked up on Black Friday, so I think I am just going to unpair these, and swap them out with the newer models. Less hassle, and I want lights turning on and off properly when I am not home. I'll probably save these ones for a rainy day, or when I need an outlet to do some quick testing with.
I also ordered one of the Sonoff USB dongles, should have it tomorrow. Though I don't know if I will get a chance to play with it before the holidays. Figured it may be a better solution than the Ikea repeater in my dead zone room, to hopefully help devices stay connected.
Any good ways to tell if a device is using a repeater or not? I know the Zigbee graph shows this with the lines, but it can get pretty messy to read sometimes. Didn't know if there was a more effective way to track repeater usage.
Just have a moment to reply, more tomorrow, but wanted to say that running two hubs really is no biggie, and was a core part of my solution. I waited way too long to start moving some of my devices back to my C7... So don't be too shy about trying that. 
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And doesn’t cost anything since you already have it. Splitting up the apps also means that you free up some resources on your hub.
This is definitely true. I am reconsidering firing up the second one at this point. My main holdout, is I was planning to deploy the C7 at my parents house with a few devices. I ended up waiting to do that given the odd behavior of the C8. I know I definitely won't have time to set this up before the holidays, but it might be a fun project to play with afterwards.
Though recently, other than these Sengled E1C-NB6 plugs, things have been pretty solid. I still need to try to repair my Ikea blinds, but other than that my other devices have been responding very well. I do think changing WIFI channels made a helpful difference. These older plugs I got a while ago for cheap, so I don't see it as too bad of a deal if I don't use them anymore. A small price to pay for getting some good stability back!
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I moved all my Aqara devices older ones back to the c7 and used the hub mesh as a stop gap and it works fine and haven't had issues with them dropping from the C7 they would not work at all on the C8 except the newer P1 Motion Sensors which work fine on the C8.
Quick update for those following my recent problems. Since I removed the older Sengled outlets, and swapped them out with the newer models, things have been pretty solid. The lighting has been cooperating perfectly, and the re-paired Aqara devices have been staying connected. One of my temp sensors may be bouncing on and off, or the temperature has just stayed steady for multiple hours (to a day) at a time. Haven't dug in enough to know for sure honestly. All of the other Aqara devices have been staying connected from the looks of things though. I'm guessing the driver change has helped with that. Jury is still out on Aqara devices cooperating fully, but so far so good!
About a week ago I was able to get the Ikea blinds re-paired to the hub. Tried the 'hold an inch away from the hub' method, and they all connected and were receiving commands after pairing. I was able to get an Ikea repeater paired as well, and stuck it between the blinds and the hub, in the same room as the blinds. The night I paired them, one was a little iffy, and took a couple commands to get it to go up/down. Though, ever since, they have been responding as expected. Think it just needed time to realize it should be using the repeater, rather than a direct link to the hub.
I did notice a couple times the last couple days walking into my kitchen a Smartthings motion sensor I have wasn't triggering the cabinet lights on. A dashboard command / or remote button command seemed to get the lights to come on, so I am thinking the motion sensor is acting up. Might just be a low battery honestly, I haven't had the time to diagnose. Hopefully I'll have some time in the next couple days to dig into this a bit more.
Also, just a side note: over the last 1-2 months I had slowly been cleaning up my hub, in terms of unused resources. Removing no longer used virtual devices, uninstalling unused apps and drivers, and cleaning up other things I used to experiment with, but never ended up fully deploying. Not sure how much of a difference it made, but I know there were probably a couple apps that were using hub resources that didn't need to be. If anything, it just helps the hub run more lean and efficient.
Overall, things have been cooperating much better than they were a week ago. Not sure if it was just the older Sengled model outlets causing a fuss with the mesh, or (most likely) a few problems stacked up making things not happy. But, between removing the older Sengled outlets, swapping out the Aqara drivers, and giving things time to settle, it seems to be working quite well.
Thanks to everyone who pitched in with advice, this community never fails to disappoint! 
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Hi. I wanted to follow up with you about the C8 hub. I tried doing what you recommended, IE, restoring from a local backup and switching my Zigbee channels to reduce overlap with the WiFi network. I also changed the batteries of my Sonoff motion sensors. All of these things seemed to have helped, and I've not had issues with them dropping off the network in a couple of weeks now. *knocks on wood.
Thank you so much for helping me out. I also appreciate that you took the time to recommend the WiFiman app, which was helpful in identifying said WiFi channels.
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You know, like any politician, I'm very happy to take credit for anything good that happens. 
Very glad things have settled for you, and remember, if problems recur, it's definitely someone else's fault. 
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