Cautiously optimistic. Installed 2.3.5.105 last night on C5 and C8 hubs. Removed an interior and exterior Hue motion sensor from my C5 hub and reset both and reinstalled both on my C8 hub this morning. Both are functioning normally so far. Previously they had immediately stopped communicating after pairing.
So, We'll see if 2.3.5.105 did the tick.
Spoke too soon, Moved another interior Hue motion sensor from C5 to C8. My newly joined exterior Hue motion sensor disappeared from the Device List on the C8. It seems that some sort of address conflict is going on.
I know @mike.maxwell is looking into it. I have 7 Hue motion sensors (4 outdoor) on the Hue bridge, connected to Home Assistant, and imported into Hubitat via the Home Assistant Device Bridge. I was planning to move them to my shiny new C-8 when I read @Tony ‘s post yesterday. I’m sure this will get sorted out fairly quickly by HE staff.
Yeah I would hold off. I've been dealing with this issue for a month or so since my initial C7->C8 migration. I've re-paired those outdoor Hue sensors and 3 or 4 INNR plugs quite a few times. Better to wait for them to find the answer than running around the yard with a screwdriver over and over again.
Can you post the model number shown in the data section of the driver for the sensor?
Sounds like what Tony brings up in this thread:
Hue Interior sensor #1 Model SML001
Hue Interior sensor #2 Model SML001
Hue Exterior sensor #1 Model SML002
All are using software ver. 42006BB7 and firmware ver. 100B-010D-42006BB7.
There is one strange thing I have noticed. If I remove a motion sensor, reset it and try to pair it again, Hubitat returns a message something to the effect "Device previously registered". If I accept that - I believe the past registration information appears. But I did not take screen shot so I can't verify that. And I do not get that message consistently.
But my C5 and C8 are running the same software ver 2.3.5.105. And 2.3.5.105 did make a difference. But did not completely fix the problems. And if I take a motion sensor from the C8 and reinstall it on the C5, it functions normally in all respects.
Just FYI. Support informed me that some (many?) of the Zigbee issues are because the C8 now uses Zigbee 3.0 and some (many?) of our existing devices startup differently than they did with previous hubs.
They are working on the issues.
Tom
I have about 10 Aqara motion sensors that will connect but then almost immediately drop off the C8. Worked fine on my previous C5 hub. I have several IKEA repeaters that helped the Xiaomi’s stay attached previously to my C5 hub. They have reconnected fine, although I have had to manually reconnect everything because the migration didn’t reconnect my devices. But the motion sensors simply won’t work, at any hub Zigbee radio power level.
I gave up with the Aqara sensors and changed to Sonoff. No problems since. Sorry that doesn't help you.
I have several Sonofs but stopped using them because the battery life was terrible in comparison and also I couldn’t get over how ugly they are. I do like the way they indicate sensing with the red led flash tho. That for me is quite a cool feature and very useful in debugging too 
I have the same problems with the C8 and Aqara devices, I have had only one Aqara device work its the newer P1 motion sensor. ALL the older versions will not pair correctly and if they do it only works for one time then it done, redo the connections tried all the radio stuff and to no avail no go. its a real problem running 2.3.5.110 on my hub.
Yes, the Sonoff's are certainly very ugly. I've not had any battery issues with them.
Yet more issues with C8 and zig bee, now my hue motion sensor dropped off line I removed and it will not let me re add it. Gee wiz I bought the C8 to improve things and now I am having nothing but zig bee issues that I never had on C7 .
I’ve had Hue indoor and outdoor motion sensors for years now and they have always been the least reliable of the 80+ Zigbee devices on my C-5 hub. They annoyed me enough that I finally put them back on the hue bridge a month or so ago. I would generally only have problems with them after a firmware update, or if I shut down the hub for some reason, but the outdoor sensors are a real pain in the butt to reset, and the only devices I’ve had to do this, with, in recent memory. I had a lot of trouble with the hue dimmer switches not staying connected, and removed all of them a couple years ago, placing them back on the hue bridge.
I’m starting to wonder if the c-8 is just exposing some weakness of hue devices, or if it is just a Hubitat zigbee bug that has been there and not brought to light due to the previous hub’s weak radio and heavier reliance on repeaters to communicate with devices.
With that in mind, you might try decreasing the power of the Zigbee radio to 8 or 12 to see if that fixes your problem. others have posted improved results with power level set to 8, which was the maximum power of the previous hub’s zigbee radio. I actually turned mine up to 20 and saw better results, I think it really depends on your environment
Possibly. Except that Hue devices are not the only ones exhibiting issues. I'm having similar problems with INNR plugs and others have reported a variety of devices. I have had Hue outdoor sensors for months, never had an issue on the C7. And I am running on power setting 8, after having tried 16 as well.
Thank you for the suggestion I will give it try but most all of zigbee devices are having issues Aqara too! It something with the c8 the c7 was no issue
There is a possible fix coming. I updated to the latest HE beta and am now adding back all of my indoor and outdoor Hue motion sensors. 
I have noticed that so far, every Hue sensor added immediately shows up as routing through one of my Sonoff Zigbee 3 dongles. These dongles seem to be much more active on the C-8. Almost everything on my routing table is going through them.
I was hoping to remove most of my Sonoff Dongles once moved over to the C8
Do you have these ones? https://sonoff.tech/product/gateway-and-sensors/sonoff-zigbee-3-0-usb-dongle-plus-e/
Those are the ones I'm using as well.
I'm keeping my SonOff on the C-8 as they appear to play better w/Aqara devices generally than HE hubs. I have some Aqara contact sensors that did not do well when connected to the C-7 until I added the SonOff dongles. My SonOff dongles, like @Ken_Fraleigh, are more active on the C-8 so for now I'm keeping them around to help w/the Aqara contact sensors, which I like very much for their small size and long battery life.
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