Are your stills PSDs? Make sure they are rendered in their own layer timeline if so. Watch for where your keyframes are in the zoom moves, etc. Maybe stretch the keyframes so that they don’t appear on the frames where the dissolves are having the problem. Also, try rendering out your stills with the moves as uncompressed MOVs (or Final Cut MOV files for smaller file size) and then bringing them back into Final Cut to do the dissolves. Just a couple of thoughts, hopefully one of them helps!
Jason Ryan