This happened to me too. I'm not sure if you took advantage of uploading your own music library to GPM, but I had uploaded around ~2k songs near Google Play Music's inception. When I downloaded it about a year and a half ago, the track file names were not only often incorrect, but oftentimes they were censored or radio edit version of songs in the export when I knew for a fact the original songs I had uploaded were the original edits.

Things have only gotten worse since the forced transition from Google Music to YouTube Music.

How can such a significant product be so bad?

The answer lies in your question. This is not, in fact, a significant product to Google.

GPM was the moment for me when I finally realized I cannot count on Google services. Since then I migrated to Deezer - so far so good, but I would not be surprised if they also turn to bad. That's why my music collection is backed up in the cloud now. I am self hosting a media server, so I am all good.

YouTube music was the worst with this too. Songs were constantly disappearing or changing