My wife has this problem with her car, it'll only take 1.2 to 1.4 gallons at a time. Every gas station attendant hates her. We've been to two Hyundai dealerships and they are clueless. The first time they said it was "Spiders", that the spiders make webs in some air valve/filter and after they vacuum it it'll be fine. It was good for one fill up.
Please see the Video, Have you ever seen this?