I had that exact problem with a sonoff sv… turns out it was a bad flash. I reflashed it and the problem (having to do the wifi reconnect) went away.
I would suggest trying reflashing which can be a bastard if they are inaccessible!
Regarding the issue with 6.4.1… yes I had the same. Total nightmare. The problem is they switched from core 2.3.0 to 2.4.2 and I had a lot of disconnects.
I ended up compiling for core 2.5.0 and OTA flashing after doing a Reset 0 (or was it 1?) in the console. That is still not quite as stable as core 2.3.0 but it’s compatible with my Fritzbox and Mesh (apparently 2.3.0 wasn’t although I didn’t have any problems)
I have 4 x S22’s and 2 x SV’s and even with the very occasional dropouts I have not yet had one offline when triggered by voice or automation so thumbs up from me.