Well, the way I read the OP's post is they checked the mobile app, they checked the gate, they checked the display in the airport. Everything said G92. And the gate even showed the flight number. Only thing that made them suspect something not right is virtually no people at the gate. Goes to the UC and that is where found it was change to 87. Apps and services that send you changes via email, text whatever are not 100% correct and they even give disclaimers that the information can change at a moments notice and to check the displays at the airport. I don't see anything else the OP could have done before getting to gate G92 that would have told them to go to gate 87 instead. A disconnect happened somewhere in disseminating the information.

Someone posted the gate change happened at 6:37 PM. Don't know what time the OP got to gate G92. As the flight was scheduled for 10:52 PM. It sounds like something somewhere did not update correctly.