Many members frequently report lesion development on the proximal aspect of the upper mandible. The causes can vary by case, but virus, injury, nasal blockage, infection, early neoplasia development are plausible guesses. An inflammatory response in the cells can occur when frequent rubbing is occurring on the skin, most commonly, that can be due to sticking their beaks through hardware cloth to get grass/treats, or pecking through metal feeders.
View attachment 2520307View attachment 2520304
Narrowing down which one of those it might be, is hard without cytological examination, but as basic treatment, you can continue on applying an antiseptic to the area, in case of injury, which apparently tends to be common. Neosporin or an antiseptic such as chlorhexidine are good as they have long residual antibacterial activity. A thorough look over your setup for any predisposing factors (such as the ones mentioned above) would also be a precautious measure.