I almost wonder if it’s an ulcer which can be caused by a bacterial infection....
Good luck.
Also, I haven’t been on MFK in probably 6 -7 years.... do they have an app or do you have to login via computer?
The pea puffer is so small that its hard to tell whats going on.
This was a recent posting I saw with a puffer mouth issue:
https://www.monsterfishkeepers.com/forums/threads/congo-puffer-mouth-problems.725077/page-3
Thinking some sort of infection...