www.makemkv.com

Noticing this in both the Windows and Linux versions, but thought I would post here since it seems to be cross-platform.

If MakeMKV is running when the system is shutdown on Linux or Windows, the shutdown will hang, with Windows showing the "Program is preventing windows from shutting down" dialog, and in Linux, the window disappearing, but the system still attempting to shut down.

After a period of time (20-30sec), an error box will appear saying "Fatal error occurred, program will now exit." I've included a screenshot of the issue.
This seems to only have started in the most recent updates of the program as I've recently upgraded my machine and reinstalled MakeMKV.

I'm willing to assist with any testing if it will help.

Based on what happens when you click "stop" during an encode, I would guess this is "normal" - the MakeMKV GUI calls the command line program to do the actual ripping, and it doesn't respond instantly to stop requests. It will attempt to finish the current operation before asking, "Any messages for me? No? I'll continue then."

Both Windows and Linux will attempt to close programs via "signals" before beating them with the shutdown hammer.