Hi tYYGH
Did you read this thread? Or further around? Quite a few possible origins for this type of problem.
In my experience sporadic problems like this are generally caused by contact problems and cleaning them (even if you’ve really cleaned all of them) may not be enough: often the problem is mechanical in the FP2, so make sure all contacts are not only clean but firm.
If you have a SD card make sure it’s configured as removable. If not, take steps to make it so.
See also here. Once it is removable, try removing the SD card and see if this makes any difference to your experience.
As to Android versions I would recommend updating to the latest available (currently Android 9 but 10 will be coming soon). See links to other info and the bug tracker on that page too.
My FP2 is currently running a beta version of /e/ Android 11 with no significant problems.