Corrupt measures
See for example #291714: Score is corrupt, seems to recover. This is one of several reports of measures having extra beats in them. I'm not sure what's going on, but this seems to be a bug that needs fixed. I'm posting this in hopes that people will be aware of these reports so perhaps we can understand why it's happening and fix it.
Comments
For people reporting corrupt scores:
It's nice to have the reports, but it's rarely helpful without information on how the score got that way. Some basic information to always include might be, what version of MuseScore did you start creating the score in (not nec3essarily what you are using now), did you enter by hand or was there MIDI or MusicXM import involved, and were there any operations you performed that seem like somehow they might have somehow caused it (typically, corruptions come from unexpected operations involving tuplets, voices, or changing time signatures).
The score in that particular issue appears to have come from MusicXML, so it's possible it was corrupt before we ever saw it. In cases like this, attaching the original MusicXML file would be useful as well.