I have a similar problem. The last few weeks (about once a week) the primary disc resets itself to factory settings. I notice because I changed the network name. Similar because of the reset the Guest WiFi also gets turned back one.
It is a real pain as I have to turn off the other 3 discs to reset the one disc as the app detects multiple discs on setup. Once reset the other discs rejoin the mesh when switched back on, other than I have to rename them again.