I tried briefly to put all my music in Google play (years ago, now) and had a similar experience.
It was terrible, and I felt like I couldn't find certain tracks very easily. I wasn't sure if this was accidental, or not. Do you know why tracks are deleted from your library?
I had no issues with disappearing tracks, but Google did helpfully replace much of my uploaded music with the "censored" versions, asking me to re-upload songs it threw away. Thanks, I'll go dig up that hard drive any day now.
It was terrible, and I felt like I couldn't find certain tracks very easily. I wasn't sure if this was accidental, or not. Do you know why tracks are deleted from your library?