have you selected roughness image in at Texture slots in texture paint mode?
Are these the same spots where you have/had your normal baking maps problems?
no not really
Is there a hole in the UV for that area?
I see you do a multiply node for the diffuse color input … It’s possible to get a value that is outside the range of the RGB values!
Just for painting, just connect the image to the input node. When ready combine them back.
which input node