I have consolidated your similar posts into one. It looks like you have been struggling for some time, now. If you are stuck at where to start the troubleshooting, please send me a private message along with your hub ID and I can take a look at your hub's engineering logs (assuming your hub is connected to the cloud) to see if I can help you narrow down the problem.
Also, this other issue with the app error that you have reported can certainly contribute to your poor experience:
I'm afraid your zigbee table does not look very healthy.
Of your nine line-powered zigbee devices, only 3 are directly connected to the hub. And they do no look to be good repeaters. For the inCost and outCost, you don't want to see values of 0 or 7. Also, the age should not be 7 either.
And if your line-powered devices aren't working well as repeaters, I can understand if the rest of your zigbee mesh (battery powered devices) have fallen off.
What are the nine line-powered zigbee devices? Brand/model (or device type). Could any of them be accidentally powered off?
Also tagging @Tony - his expertise at interpreting this table exceeds mine by several logs!
P.S. Although Sengled bulbs (and their first general outlets) are line-powered, they are purposely designed by the manufacturer not to repeat.
There was a time when my automations didn't run well. And of course, it turned out to be poorly constructed zigbee and z-wave mesh networks. @bobbyD gave me ton of advice on fixing my z-wave mesh, while others (@Tony, @ogiewon) gave me advice on fixing my zigbee mesh. It took some time (and a few new purchases - I learned that all repeaters are not equally good), but both my meshes are very performant ever since (going on ~3 years now).
I've pasted a screenshot of my zigbee mesh below. Under the neighbor table, I've highlighted (with green dots) the zigbee repeaters that seem to be better than others. And, as you can see in the route table, with two exceptions, those are the repeaters used by end-devices (red dots).
Notice that "Repeater - Sonoff" and "Washer Light" both have inCost/outCost = 1, and each repeat to 4-5 end-devices. In contrast, "Outlet - Back Porch Lights" has inCost/outCost = 7, and isn't used to repeat to any end-device.
There is no magical wand to fix a mesh network, outside of being careful with device choice and positioning. And ensuring that power isn't cut off to line-powered devices for extended periods.
That sonoff repeater is a star! Still can't get mine paired, except to a dev C7 with nothing on it.
Anyway, what brand is "Washer Light"? Also seems a great repeater
Agreed. Jasco/GE Zigbee switch.
The Sonoff is a star on both my zigbee mesh networks.
How do I send a private message?
click users name/picture/icon
I have/tried one thanks to @aaiyar and it is very effective/active as a repeater, excellent stuff.
I agree with @aaiyar's assessment of your Zigbee table; the only neighbor device that seems to be capable of routing is the device with short ID 4836; yet even its link status is marginal (inCost & outCost both high indicating the hub doesn't 'hear' it well and the device similarly doesn't hear the hub well).
And it's showing null where you'd expect to see the device's label; AFAIK that's kind of a limbo state you typically see when a device has rejoined the network and not yet gotten matched up with its original paring information (if you refresh the page after a while this device may show its label instead of null). Devices normally don't need to rejoin unless their link is broken.
I'd approach debugging something like this by first taking inventory of what (if anything) is stable/working and what is not. Do the devices listed in the child section of the table work reliably? They don't involve repeaters since the hub talks to them directly so they should work regardless of the state of the neighbor table. If they don't, something is amiss with the hub, or else there is some pervasive environmental issue (noise or something blocking the hub's signal) that is affecting everything.
There's always a chance a rogue device could screw things up; if all else fails, power off your repeaters and see if just the hub's child devices start working. If they do, try adding a repeater into the mix (the neighbor table should show pretty much immediate improvement); if not turn it off and try another repeater.
At the risk of trying your patience, could you answer a few questions for me?
Thanks again for your help.
Please check your messages in the upper right, I sent you a message.
You cannot predict if a device will connect directly as routing is based on your specific environment, distance between the hub and the new device and obstacles that a device will need to avoid (such as walls, glass doors, etc) to reach the hub.
A good way of avoiding bad repeaters, is making sure the device is on the Compatible List of Devices. Also browsing our community for the specific device model BEFORE purchasing it, is another great way to avoid devices that are known to be problematic.
Not a problem. But everything below is zigbee-specific.
It will appear as a direct child device under the "Child Data" section of the getChildAndRouteInfo page.
In my experience, most zigbee 3.0 devices are good repeaters. I am particularly fond of the TuYA USB zigbee repeater and the Sonoff CC2652P zigbee USB dongle re-flashed to be work as a repeater.
To add to what @aaiyar said, here's a link to a post I made a while back with some info about the getChildandRouteInfo table. 99.9% of HE users won't find this useful 
so Hubitat doesn't document it, but questions about it pop up from time to time: Zigbee issues - #22 by Tony
Just a little bit of typing in the search bar in this forum can be very profitable, for example below searching on "good repeater." You can add in specifics like "Z-wave" or "Zigbee" to further target your searches. 99% of the time any question we come up with has been asked before, usually multiple times. 
This is super useful. Is there an overview of how to interpret this file ( getChildAndRouteInfo) . I am having the same issues, and when i read the file I can see that I have a very unhealthy zigbee mesh... what I don't know is how to interpret the different parameters so that I can better find a solution.
Main questions are:
Where do I see if a device is connected to the hub directly or to a repeater?
What does the Age mean?
What does inCost and outCost mean
How can I tell how many "hops" there are between a device and the hub
Backstory for me is:
I moved house and brought with me a lot of the devices... after some expected instability for the first few weeks, everything stabilized. Now after 6 months of working flawlessly, i have having issues.... I have subsequently removed most of the mesh, and am starting to rebuild it, but want to know how to understand the file, so I can make better decisions (or diagnostics) during the rebuild.
If you are using zigbee repeaters (or any other mains connected zigbee device) does it have to be paired with the hub or just powered on?
Thanks.
Has to be paired with the hub.
I think I finally get the idea of a Zigbee mesh. Thank you so much for your help. All my devices seem to be working properly and, if I have troible again, I now know where to look. I owe you a dinner the next time you’re in Ft Myers, Florida.
LOL - I had to read this a couple times, at first I thought you were trying to correct his grammar! 
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