Had this happen today 1-2-2022. (2013 Model S85). When attempting to open the charge port door (using UMC, touch screen, and mobile app), could hear the mechanism click, but door would not open. Solution was to use my fingers to apply some pressure towards the rear (right) side of the red plastic charge port door, while simultaneously using the mobile app to open the door. I think it's just a function of the spring in the charge port door hinge getting weaker over time. Might be time to replace it (again, had this replaced once before some years ago under warranty). In the past, if I've waited a while and tried again, the door would open. Note that other posts describing the manual release are for cases where the UMC is stuck connected to the car, and not for cases where the charge port door will not open. And on the original Model S's, there isn't anything to "pry" open that wouldn't risk damage.
