After upgrading from v3.11f3 to 3.11h, the first run encountered an error.
File: y:\projects\_main\szipfile.cpp Line: 343 Term: pfileIn != NULL Code: 0x00000000 The application encountered an unexpected exception and is in an undefined state. Please close the application and send the file C:\Users\user\AppData\Roaming\Mp3tag\Mp3tagError.log
I didn't try much, but attempting to tag my files with a script wouldn't work (tag sources buttons wouldn't do anything, no popup, no activity, just a broken button, the whole UI probably was dead at this point). I restarted the program which unfortunately overwrote the log file so the above error is all I have.
After restarting, the program seems to be working fine again now.