Alright for the sake of reference so you'll have an easier time here are what each class looks like normally vs with the bra of holding
Fighter:
Rogue:
Mage:
Personally I think Rogue is the hardest one to notice, since they're always facing away from camera, but once you know what to look for it's pretty easy to spot
also in story mode who has a bra of holding tends to be predetermined, so you can just memorize which character had it last time you failed
Hope this helps