UA is well-known to pull fast ones on customers when it comes to delays. There is a flight history, but somehow that is either not fully visible to agents or when plane swaps occur, that gets erased. Had a case where the inbound flight went mechanical (cancellation, took screenshots) then UA assigned a new plane that arrived 2 hours post departure posting a 2.5 hr delay which was then further exacerbated by weather to a total of 4 hours. UA flat out refused rebooking - due to weather (not covered). Had to buy a walk up ticket to get on my way and ultimately a DOT complaint to get it sorted. It always pays to have screenshots when UA starts lying to the DOT … once you send these in it get settled very quickly.