I had exactly the same problem, after a full set of replacements and hours wasted with their tech support over a 6 month period I sent them back and bought the Deco M9s which have not skipped a beat.
I have this and one of them never plays well with the other 2. I've reset them repeatedly and even switched them around but it's the same one causing the issues. Read the reviews and if possible, get a router with better coverage (ie: solve your problem a different way)!
Check the firmware version you're on with any Velop products. Linksys have pushed out some very dodgy firmware in the past that can cause dropouts. I would recommend that you also turn off the automatic firmware updates, just check the app every so often for newer firmware. When the firmware is released you can then do some searching around to see if other users are having issues with it.
Nope, I do this whenever I get a new router. Your device doesn’t keep any record of the MAC address of what it connects to
I know a different brand, but set the network name and password to the same as my BT router for my TP link deco M5s. I then turned off the wifi on my bt router. This just saved me updating all of the passwords on all of my connected devices. Seems to have worked, but every so often I do have connection drop outs. Do you think this could have caused an issue?