Musescore 4 deletes notes and bars after saving and reopening

i have a due date today (4/5.01.) but everytime i save and reopen the file, most of the things I did the day before are messed up completely. wrong rhythms, random notes in between my melodies are missing, bars have 8 quarter breaks even if the bar is only 4/4. i have spent several sleepless nights on this now but i just cant find a solution. i am desperate. can somebody help please?