Each girl has 7 outfits: casual1, casual 2, gym, swim, sleep, custom1, custom2 & custom3. The first 2 can't be modified by user input and those are the only ones I touch. User directed wardrobe modifications have always been a little buggy even in the base game (its not uncommon for them to lose custom pants & panties when you exit the interaction menus)
Could you try building a few different custom outfits, assigning them to different days, then letting time pass to see if they're actually wearing them on days they're assigned, or if they're wearing default stuff?