Issue: United* app & online gate check (Google) gave me a false gate (D1 instead of D26) in the middle of boarding.
Resolution: Confirmed on a flight the next day, all is well except I'm in a middle seat.

Backstory: I screwed up my times (thought boarding time was flight time) and found myself rushing to the gate. As I was on the "mobile lounge" from the terminal to D gates, about 5 minutes after the posted boarding time, I got an app notification that my gate was changed from D26 to D1. I then checked the internet and it confirmed gate D1. So I bum rush to D1 to find it completely empty. I meander over to a high C20's gate and confirm the gate... and she tells me it's (still) D26. I miss my flight and get rebooked. Let me just say that I know I made some critical mistakes, so this isn't me trying to throw all of the blame on UA. It didn't help that I was at the Five Guys in the B gates needing to get to D1/D26.


Primary question: Is this a known issue? Has anyone experienced something similar?
Second question: I went running to a gate agent to ask them to call ahead and tell them that I was coming. She basically ignored me and told me that she can't/isn't supposed to do that. I've seen them do this before and she was quite surly otherwise. What's the story?

Edit: I wrongly called it the mileageplus app. It's the official United app for android.