Super helpful, Kacee.
What's your routing back from DAR to SFO? You probably cannot book that through Europe, as crossing two oceans on a single RT is now supposed to be illegal.
Maybe that is the issue then. Pretty much everything that came up on United.com from DAR back to SFO routed through IST or else CAI--all trans-Atlantic. But United.com lets me book the itinerary, so what to think?