I'm still trying to isolate WHY it's happening, but I've narrowed it down to one of the two cases

Under the BetterWardrobe_ListData saved variable where the outfits get saved, new sets (and saves to existing sets) do not create or update the "sources" key.

Alternatively, it may be that the intent to use the "itemTransmogInfoList" key to generate the thumbnails, but have not yet converted it over.

(I have been trying to track this one down all night, but without knowing which is the reason for it, I'm at a loss at what to look for)

It could be that it just needs a data refresh and to update the display.