iPhone Music shows wrong album covers

I have a "Music" collection of exclusively own CDs and own microphone recordings as .mp3 audio files. I added a cover image to the first title of every album to keep the file size of the other titles in the album small. When I "Sync" the complete Mediathek to my iPhone the first time often many album covers are missing, they show the light gray "Music" icon of two eighth notes. A second "Sync" with the same data, corrected this and all my covers (several hundreds) were shown on the "Albums" list correctly, each album showed the image of the first title as intended. I observed another bug: when I add/change a cover image of a title, "Sync" will not recognize that the file has changed. You must change either the title name or something else in the "Information" to update the file on the iPhone. But these are minor bugs, which I can tolerate.

Since my recent iPhone 13 update to 26.3.1. (liquid glass) however, many albums now show a wrong cover image from a different album of my collection, which is totally inappropriate. All "coverless" titles show now the same wrong cover image instead of the "Music" icon. Only albums where all titles have added a cover image (the same for all titles) show the correct image. If I would do that with all my titles it would cost me 1,2 GB additional wasted iPhone memory and many hours of manual editing all the cover images.

The album covers were shown correctly on my MacBook. I then tried recreating the "Music" Library new from my audio files without success. In Music Preferences the option "Coverbilder automatisch aktualisieren" is disabled. After "Sync" the same happens, the bug persists. Since I read here that these cover images have made software problems since years, I think we should name it the "Apple iPhone Cover Image Bug".

I appreciate, that titles without covers were attached covers automatically, but it should be a cover from the same album, and not a random image from another album. Any workaround would be highly welcome.

Bernhard