I have all my music in iTunes on my old iMac. Or I did have. I created several playlists years ago and each of them had 30-50 songs in them. Tonight I opened iTunes and clicked on the playlist and each one had only 3 or 4 songs. Where could all my music have gone? I haven't changed systems or done anything like that recently. I'm running High Sierra.
While searching elsewhere for my music I decided to check my iPad Pro. My music appears to have gotten transferred to my iPad. I feel confident I didn't intentionally do this so some settings on my iPad or iMac must have triggered moving my music to my iPad. My iMac hard drive is about full and my iPad has 200 GB free. I don't know if that matters.