Album cover lost in sync

When i add album covers to my iTunes library on Windows 7 and then sync with my iPhone ( 64Go, if that matters ), covers are lost. The weirdest thing is, if i play any song i did add covers to, the cover shows in the back. But it won't show in the album tab. To make it simple, it seems like songs do have cover, but the album doesn't. ?_?

I tried :

- Using older / recent iTunes

- Restore / Update my iPhone

- Reboot computer / iPhone several times

- adding covers in the iPhone instead of the library

- changing image extension for the cover

- changing resolution

_Somehow, a cover did work on an album, and after several sync, it just disappear, but as i was saying, songs do have covers when played, but the album cover doesnt work. It's just blank.

I spend several hours on my computer / internet trying to solve this, in vain.

Need help :c