Hi came here to say , I have sporadically seen similar issues with these devices and other sonoff devices,.
After it all came to a head recently, the fix was to remove a dongle-P (flashed as a router with latest router firmware) from the network. They havent skipped a beat since.
My co-ordinator is a dongle-e. I use ZHA.
Reading some posts above I wonder if there is a zstack issue or a TI related issue but the dongle-P is in a drawer, maybe it will return as a Thread device some day !
ps. I had an automation alert if a thermometer gave me the exact same reading for 6 hours or more so I knew to go and re-pair the thing. I think this is no longer needed now I found the culprit !
pps. actually when I removed that router, I had 3 stuck thermostats. I only re paired 2 of them, the other just started working I noticed. I was just in the zone so used to re-pairing them. My network now seems to self heal, it didnt before.