Since updating to V 8.1 I see the following odd behaviour that seems to be related to your problem:
I am using V 8.1.857 on Windows 10 Pro, Version 20H2, build 19042.630.
When I try to exit the program using the X (top right on the menue bar), the program window closes but the background process (Hintergrundprozess) remains open. When I then try to launch eM Client again, nothing happens. I have to manually quit the background process via Windows Task Manager. However eM Client doesn’t seem to “like” this and starts a lengthy database check every time I start the program, saying the program was not shut down properly.
This does not always happen, but more than half the times I exit the program.
It seems that exiting eM Client via Menue>Exit works more reliably.
Could it be that an old bug is raising its ugly head again?
I opened a ticket with support today and am looking forward to their reply.