Lots of album art not transferring from Music on Mac to newer iphone / inconsistent behavior within Music and ios Music.

Bought a new iphone (biggest capacity). Have a large library. I load music to phone by making a playlist (30K songs) in Music on Mac and sync playlist to load to iphone. I am finding a lot of album art is not showing on iphone. Sometimes on the phone it DOES show on the what is playing view for every song of an album, but doesn't show in the single album or multiple album under an artist view.

Album art does show on Music on Mac main list view, but SOMETIMES under "get info", it shows nothing. If it DOES show art under "get info", I cant delete it, to replace. I can only add to existing. I asked this question in another post as this used to be a feature by right clicking on art, and hitting "delete".

Fixing/replacing the art in MUSIC on Mac, and re-syncing doesn't usually fix on the phone, though a rare few times it WILL update the phone files- but not usually. Usually I have to take files off phone, and reload them. This has been a problem for years with older phones also.

The only way to truly fix seems to be removing album from phone entirely, removing same files from Music entirely, using third party metadata app (Metadatics) and removing old art, adding new art, re-adding album to Music, then adding back to playlist and re-syncing to phone. this is highly time consuming as I have a huge library and its happening to a fair amount of random albums.

Dont understand why so much inconsistent behavior within Music on both Mac and Iphone but biggest annoyance is just not showing the art on the phone, that often seems to be there. Am I missing something?

Why does album art show on random album/files in Music on Mac, third party metadada apps, but wont load to iphone for some albums? Really frustrating when its hundreds of random albums, that were fine on old phone.