classical guitar score crashes entering sextuplets

Hi, I have a score almost completed, but I'm unable to finish. Infuriatingly, it crashes every time I try to copy/paste from an earlier section in the score. It also crashes when I delete the measure and try to manually enter the sextuplets from scratch (press 5 to get quarter notes, then Ctrl+6 for the septuplets). Musescore won't accept either, and crashes instantly. I have tried deleting measures, Ctrl+delete. I tried the repair plugin, and it says no corruption. I don't get any error messages on saving where I can look up the details, either. Any insights would be helpful. Thank you! NOT FOUND: Bittersweet.xml