I can't believe nobody else is having this issue. I too have the same problem. Images I uploaded on the web were synched to my FTM file, however at some point they disappeared on the web. Now they are only in my FTM file on the PC and not on the web. Online it just shows the generic ancestry.com image, but the item is still listed. FTM shows everything is in sync, but clearly it's not.!
There has to be a way to force it to re-sync changes even when it thinks they are in sync, but I can't find it.