A bit of a better picture, i circled the part of his mouth i’m concerned about. haven’t been back yet to get any more pictures

[Smxo]

of a

 

[kinyonga]

I'm not a vet and am just giving my best guess...
The little dark mark along the edge of the lip in the red circle could be the beginning of mouth rot. The photo isn't clear enough for me to tell anything else.