My New BP have a weird brown stain, do you know what it is?

[LGSnakes]

Hello Everyone,

I've welcomed my Banana Pie Bald PB Naga In March 28th 2019. He was born in November 2018, Eats frozen rats pups, had his first meal on April 9th. He also had a perfect shed on April 2nd. I put him in quarantine for 10 days before putting him to his new enclosure.
I use a heat mat with a thermostat (90 degrees), he has a cold and warm hide, water and a humidity box with moss in it. His set up is in a plastic container and I check the temperature and humidity level every day (70%).

Today I saw a weird brown stain on this body, and the scales look like they are not on the same level than the others. It looks like if it's dry (kind off)
I tried to clean it but it doesn't go away. I have no idea what it is. I want to add a picture but I can't figure out how so here are the links of the 3 pictures I took:

https://ibb.co/s90ph48
https://ibb.co/2K7xvNs
https://ibb.co/2K7xvNs

Any idea? Suggestions?

Thank you

[Toad37]

From the angle of the picture it just looks like some stuck shed. U can give him a warm soak (aabout75-80 degree water) and it should come off no problem.