I lost some bars out of nowhere and how can I get them back?

I opened a file of a score I've had for a while, which I'd been looking at for over a year. I opened it after updating the Musescore Studio program, and now that I look, I can't find a large number of bars, only two 6-part voices. Why did this happen? Is there any way to recover the version I saved before opening it today? Thanks.