Corruption/Critical corruption and crash when dealing with local time signature of 12/8 in 4/4
To reproduce the picture above, drag a 12/8 local time signature into a staff and then go back to 44, at the bar right before going back to 44, type "6." for dotted minim (rest). This will somehow mess up musescore as in in the image.
One way one may resolve this issue is by Cltr+Del the bar with that error(second bar top stave), however, doing this results in some really funny rests shown in the image above and the file cannot be reopened.
I found out that one can resolve this issue by having a second 44 time signature in the 4th bar and deleting the 2nd and 3rd bar together.
As a bonus, one can press "8" to cause musescore to crash even though one expects musescore to tie the note to the next bar. At this point the best way to mitigate this critical corruption error is hope that Cltr+Z works and musescore didn't crash(it crashed once during one of my tests but I'm not sure why)