Cover does not display properly

[lyapounov]

I have a folder Cantates [Gardiner]
It has 56 subfolders
CD01 For Christmas Day BWV 63, 191
CD02 For New Year’s Day BWV 143, 41, 16, 171
etc..
till
CD56 For the Sunday after Christmas Day BWV 225, 152, 122, 28, 190

All flac files.
No flac file contains a cover inside the file (I have checked using Metadatics)
All subfolders contain a Cover.jpg file
When browsing the content of the top level folder, all subfolders images are correct

But when I open an album and look at the track images: CD01 is correct, CD02 is correct, CD03 has the image of CD02, and all other folders have the image of CD01

This whether I use Lumin, Teac HR Streamer (which is the same), or Kazoo control point...

I have reloaded the entire library, rescanned, etc... same phenomenon...

What could that be ?