Playlist Not Saving or deleting songs

I’ve read dozens and dozens of older messages regarding the same issue and troubleshooting suggestions. I’m working on a brand new iPhone 16. I have an Apple Music subscription. I spent over an hour creating a (work related!) 40+ song playlist last night, and now today only 11 songs are in the library playlist. I try adding the songs again from the playlist “add music” and the pop up saying that song is already in the playlist appears. Ugh!!

So, then try searching from Apple Music for the song, then download and add to the playlist. Same thing.

Soooo frustrating.

I don’t know what AV software is (from someone’s suggestion), so don’t know how to begin with that…and from my phone rather than the comment which was meant for a computer user.