Please describe step-by-step what exactly you are doing.
Imagine how we try to reproduce these steps in our environment. We therefore need to know exactly what kind of files you are loading and how exactly you "make and save changes in the Tag Panel".
Example how I add the same cover for all tracks of a new album:
- I load the entire album with mp3 files into Mp3tag
- I select all tracks
- I drag & drop the JPG cover from my Windows Explorer into the Tag Panel of Mp3tag to the Cover Art area in the lower left corner
- I press Ctrl + S to save the visible cover art into all the selected tracks.
For what kind of music files you see the cover art disappearing?
How big is your cover art?
What picture type has your cover art?
As we have already asked you before:
Please be more descriptive, also in what you’ve already tried.