Sometimes when I enable the WiFi hotspot, the FP3 reboots immediately. This never happened before the upgrade to Android 10 but occurred a few times after the upgrade.
Today I had this issue when WiFi was turned on (and connected), mobile data was on and bluetooth was on. I pulled the notification menu from the top, tapped the Hotspot icon, and the phone rebootet instantly.
It happens only when switching wifi or hostpot on? You did not observe reboots at other moments? (In which case it should go in the following thread, which you could of course have a look at:)