Musescore crashed and new session did not save work after starting a new session. Is this normal?

I'm pretty distraught at the moment because I spent a number of hours transcribing two songs tonight and my work is gone. I don't rely solely on auto-save for either documents or music; I regularly save my work throughout the course of any project so I'm confident that failing to save is not what's brought about my problem. I exported both pieces in question so I have the PDFs but I wanted to nudge a few things and the scores were not in the same shape I'd left them. Nowhere near it, I'm sad to say.
The first was one that I'd started a couple weeks ago and finally made it a priority to finish. The second is a project that I just started same day. The first song comes back exactly as it was last saved (weeks ago) MINUS the 4-5 hours invested today. The second song reached a point that I'm not confident is even close to where I was when the program crashed at some point in the early morning. I started a new session of the app, continued working, finished both pieces, exported them (again, saving regularly). Back-up files have the 7/6/2019 version of the first song and nothing of the new piece. 'Open Recent' returns some cryptic names that open both of the files in question, but only to the woefully incomplete status mentioned previously.
Aside from venting and maybe receiving some commiseration, I'd like to know if this happens regularly. And HOW ON EARTH this happened at all. And WHAT ELSE I can do to avoid this in the future. Both songs played through completely in the software with no problem. PDF uploads won't convert back to Musescore - they're both jumbled crap. So my work is freaking gone.
Advice appreciated. Tissues, too.