Second time i got this reported but i couldn't reproduce it, last time it was mentioned IIRC the user had an issue with Flash drives, because there were 2 visually identical ones but only one of them fit the quest
Mind you - this feature may not affect custom traders.
Hi, have been playing raids, didn't restart game after first try and now it has started working like normal again, maybe got unstuck when I gave and actual FiR item to a random quest, bought the rest and now it suddenly accepted the items, no clue why but at least it works for now!
EDIT: Seems that the same quests that did not accept them still do not, but new quest(s) I got it worked fine.