Entire file suddenly metrically FUBAR'ed---Help!

Hello Everybody!

I have been really enjoying this software. It has been working very well, until today. I'm made some edits on a score, specifically time signature changes, and adding/subtracting bars. Now the entire middle section is suddenly metrically jacked! Measures have both repeat signs and rests, eighth notes are dropped, and phrases have been pushed over barlines. The piece is long, as as such really slows Musescore down, and causes greater instability.

how can I rescue this piece? I have the correct spacing in other saved backup sessions--does anyone have any advice about how to stitch together multiple musescore files without having to re-copy and re-paste at EVERY SINGLE time signature change?

Thanks for reading my post, I'm open to any and all suggestions. I have many, many hours into this piece and need to deliver a score in a few days.

-Kip