Hello,
hope my English is fine in this Forum and hope that problem is in the correct section!
Have following Problem: since last week I have installed OMV (Version 3.x) and the minidlna plug in as well . So far so good as all is running well. Videos, mp3, jpeg will be displayed or played.
I habe stored all my mp3 in specific folders. Each folder contains a CD and contain all songs as well as the thumbnail of the cover. This is valid for all my 105 CD's. But not all thumbnails will be shown on the clients (Mobile phone, TV).
Example:
Art on noise: no thumbnail will be shown on the clients (thumbnail is available)
ABBA: thumbnail will be shown
The size of both thumbnails are the same and both are jpeg's
Now it's geeting strange:
If I'm deleting the thumbnail of Art of noise and copy the thumbnail from ABBA into Art of noise folder no thumbnail will be shown (from ABBA) as soon as I'm playing Art of noise songs..... this is very strange. The ABBA thumbnail in the ABBA folder will be still shown. 
This behavior is given at some CD's not on all. The majority are showing the thumbnails but some not. Is this a bug of minidlna or is there a workaround given?
Any support is highly appreciated!
Rudi