Apple Music MacOS does not sync artwork to Music on iOS

Since I moved to a new MacBook Pro (MBP) Apple Music is causing a lot of problems with my local library. To fix them I checked all my audio files and embedded the album artwork in the audio files themselves, instead of trusting Music to link it correctly (it didn't).

Now I still have problems syncing my library to my iPhone: although all tracks have artwork embedded in the audio files, this artwork does not show up in Music on my iPhone. I already tried the following:

• deleted all audio from my iPhone, using the storage settings, and resyncing with my MBP
• deselecting all tracks from the sync settings on my MBP, syncing to empty the iPhone, selecting all tracks again (I use a playlist for this) and resyncing the tracks to the iPhone again
• making sure that all albums show artwork in the Music Album View on my MBP (making sure that the Music cover art cache is filled correctly), resyncing to iPhone --> this actually fixed a lot of album art, but still a number of albums are not showing album art on my phone
• removing individual albums from the sync, resync, add them again to the sync, and resync again --> didn't not show the artwork

After all of the above I'm still stuck with specific albums that don't show their artwork on my phone. All these albums have artwork in the audio files of their tracks. Both AAC and MP3 files are impacted. I'm out of options. Any suggestions are appreciated.

Versions: MacBook Pro M1 Pro, MacOS Sequoia 15.3.1, Music 1.5.2.56, iPhone 13 Mini, iOS 18.3.1.