I doubt that I’ve done something wrong with my setup - Thread just seems to me like it isn’t where it needs to be. I have Zigbee, Wifi and Matter over Wifi devices that have not failed me once. The only devices that fail me constantly are Thread based devices. I’ve tried using a dongle as a TBR which died on me and an M3 hub which acted as my replacement TBR. In both scenarios, I’ve constantly had to reboot the routers to get devices to reconnect, only to then find that all of them disconnect again except for maybe 1 or 2 devices. Issues can be described as either being unreachable or still reachable but not reporting any status updates (i.e, a sensor staying closed when physically opening). My advice is, do not cope and attempt to troubleshoot. Just stay away from Thread - it is complete and utter trash. I’ve already replaced all my sensors with Zigbee variants and haven’t observed and failures. And thank Christ for Matter over Wifi devices because it is far more reliable than matter over thread.
I have no issue with my Matter over Thread, but I had when I first added Onvis S4 smart plugs.
Onvis have recognized that the smart plugs have a bug that makes the stop relating messages, but still accept the messages, so they act as a black hole.
There is a firmware update available, but it requires an Apple Matter hub, which then per default makes the Onvis S4 smart plugs an Apple-only device, even though they advertise it as a general Matter device.
No issues at all with my Eve energy Smart Plugs and Aqara U200 Smart lock and some Aqara door/window sensors. Using a ZBT-1 dongle with my HA RasPi 5. In contrary i have quite some issues with my zigbee devices and will replace them over time with thread counterparts.
Maybe something wrong with your setup or choice of thread channel ?
I think Matter, and especially Matter over Thread, are far superior to Zigbee in every aspect:
Easy setup and device registration with QR codes or numeric codes, convenient sharing between different ecosystems (Apple, Google, Amazon, Home Assistant), slightly better security and encryption than Zigbee, and multiple transmission paths (Wi-Fi, Ethernet, and Thread).
And last but not least: if there is potential radio interference on the Thread channel from neighboring Wi-Fi or other Zigbee/Thread networks, you can simply change the Thread channel and all devices will switch with it. With Zigbee, you have to re-pair all devices, great!
On the M3 Hub which I was using solely as a router, it said it was channel 11. And I didn’t seem to have the ability to change that. Can’t remember what my old Dongle’s channel was. Are you saying that a channel change could potentially resolve those types of issues?
Channel 11 is used by potential other Zigbee/Thread networks as well as wifi channel 1-6 roughly (depending on the channel bandwidth in the 2.4 GHz network e.g. 20/40 Mhz)
I found this helpful to identify possible radio interferences:
Its german, but you`ll get the idea: funk = radio , kanal = channel, Wlan = WiFi
So, if your Zigbee channel is set to 11 and your 2,4 Ghz WiFi to channel 1-6 you are going to have 2 possible sources of interference in your own household, let alone possible neighbours.
Could OP please list brands/models and firmware revisions of the troublesome devices? As others mention, could be Thread’s growing pains, could be an avoidable firmware bug.
I have several Zigbee devices, wired & remote, and in my recent home Internet provider switchover joy they were the devices that operated while the Wi-Fi was down. Would love to hear specifics about your experience with difficult Thread devices.
I started out with Aqara Door Sensors. 5 of them. As well as some Motion Sensor P2s, and a single Color Light Bulb (recently released). As well as two U300 locks. So roughly 10 devices.
How many of them were battery powered?
Okay, so only 1 device that acts as signal extender (light bulb), all others are passive battery devices.
Which channel are your zigbee and WiFi 2.4 Ghz on?
You should make sure that Zigbee and Thread are set to different channels. They can be on neighbouring channels like 11 +12 without interfering each other because Channelwidth is only 5 Mhz for Zigbee/Thread Channels.
You might also make sure that your WiFi-Channel for 2.4 Ghz is set to a channel as far away from your Zigbee/Thread channel as possible or switch from 40 Mhz to 20 Mhz channelwidth if necessary.
After that you have a situation that at least your own radio networks wont interfere with each other.
Next you should take a look at the distances of the battery devices to the next Thread Router (Hub, Light Bulb): more than one room apart could be a problem for Thread and Zigbee as well.
If all of the above is in the green zone and you still got problems with your Thread Network come back and send your Matter devices over to me! 
Zigbee channel = 25
Thread Channel = 11
2.4ghz wifi = 6
5hz wifi = 48
6hz wifi =117
I thought about buying more thread border routers (more m3 hubs potentially) to increase the hub cluster but it just didn’t make sense to me how everything would crap out. I’d understand if the faraway devices crapped out intermittently but every single device was going offline or just not responding.
To answer your Q about the bulb, the TRB was on the main floor near the back entrance. The light bulb was in a cold room in the basement, which is on the opposite side of the house. Compound that with being a floor under. There’s also an FP2 which is in the basement kitchen. One floor under the hub but on the same side of the house.
How many of them were battery powered?
6 of them (5 sensors and 1 motion sensor).
I haven’t seen anything lately, but as of last January, having multiple TBRs is/was not recommended.
It’s fine, thankfully “Thread” does not dominate the market for functionality of devices. Everything I am doing at home at the moment can be achieved through zigbee/matter with wifi.
@DocMarc73 if you’re genuinely wanting those thread devices that I have I don’t have them anymore since I tossed them away. Garbage pickup grabbed it already.
Okay, i didn’t get that you literally threw them in the bin. So you threw away technically working devices ? Interesting attitude … 
Whatever. Paramount it’s working for you.
I must admit, that there are some really bad matter devices on the market, that force you to register with (chinese?) brands and their clouds to get them fully working (e.g. Nous and others …).
But fortunately there are enough more trustworthy european alternatives.
Buy cheap, buy twice …
Im out, take care!
It’s a bad habit of mine. When something doesn’t work, I get pissed off and throw it out or literally destroy it into smithereens with a hammer. I’ve got to vent out my frusturation somehow - and it’s better than physically taking it out on my wife or kids.