How many UniFi Access Points do you have? Just pick 2.4GHz channel 1 for the first AP, channel 6 for the second AP, and channel 11 for the third. Remember to set the channel width to 20MHz to create those open gaps for Zigbee/Thread to operate within without conflict.
If you have more than three APs, then start reusing channels 1, 6, and 11 again, but try to make sure the two using channel 1 are far apart from each each other, etc...
Zigbee and Thread both operate within the exact same frequency space, and are both managed by the same team. Thus, if you constantly had problems with Zigbee due to RD interference, chances are good that you might also have a hard time using Thread.
Personally, I find Zigbee much easier and more robust to use versus Z-Wave. I have zero Z-Wave devices (yay!) and could not be happier.
It is good to have so many options available on Hubitat!
I think this was at least part of the answer. I currently have 2 APs. I will likely end up having a third at some point, but I'm not really in a hurry there. Two seems to be giving me decent coverage. So I set the UDR on Channel 1 and the U7 Lite AP (meshed) on 6. Most of these bulbs started coming back to life. At this point, though I had taken two bulbs out, I could not get them to go into the fabric again. I don't know if the radio on the Apple TV was frozen, but I ended up resetting both of them. Once I did that, everything seemed to be working as intended again.
Interesting, I did not know that!
I don't know if I would say I had consistent problems with Zigbee, just a lot of little annoying things that got on my nerves. I just never really felt it lived up to the hype. The little bit of Zigbee 3.0 stuff I had was fine, but by the time I got those, I had already decided Zigbee was on its way out.
I know I am a black sheep on this one. I've never been a big fan of Zigbee; Z-Wave has always been solid for me, and it's gotten better with LR.
I'm still not overly sold on matter. I'm willing to play with it in certain limited applications, but it still isn't my go-to.
I am a firm believer that one should try to pick a brand or a group of brands and try to stick to those families. In my case, I'm mostly Zooz, Inovelli, and Ring on the Z-Wave side and Nanoleaf and Tapo on the Matter side. I'm not saying not to experiment, but the more variables you have, the more opportunities for problems. I took advantage of the Father's Day flash sale. Once that hub arrives, I will probably repurpose my current device's hub as my new beta hub. I'll keep the radios on on that one and use that hub for any new devices I want to experiment with.