Score corrupt, musescore crashes when saving repaired file.

Hi there, first of all, thanks a million for this wonderful app and the resources you provide here.
Yesterday I downloaded a score and made a lot of changes to it. Everything was ok until this afternoon. Tonight, the program suddenly crashed upon playback.
It says measure 20 is corrupt and it indeed has 5/4, I have no clue how that happened.
All steps provided here don't work for me: https://musescore.org/en/node/54721
- How can I simply correct the rest length to 1/8? I can do that but the measure will still contain 5/4 in total.
- Switching voices hence and forth doesn't change anything.
- Deleting the bad measure entirely works but then the program crashes upon saving and all is lost.
Help would be much appreciated!