monster sprite is jumbled in ff3usme

I'm not too sure what could have happened off hand. What kind (size and format) of monster sprites did you import, and over which sprites? Have you checked in battle to see if the sprite is indeed messed up? I'm sure it is, but if the atma editor shows it's okay, then that's kinda weird. How much free space are you showing in the atma editor?

Did you have a lot of work done? If not you should start over and make backups frequently and just be careful and check often to see if it happens again so you know what caused it.