randym77 posted at 11:05AM Sat, 29 August 2020 - #4397902

Does it work if you start with the model's mouth open?

Yes. That's how you can tell it happens instantly - you can look at the mouth and the moment you upload it the moment that issue happens on the model you just uploaded. That is to say, the model you have open right now ALSO develops the problem, not merely the copy of the model saved to the library.