Did you figure out what this was from? Just noticed my largest chick has something similar and I am also using the Premier1heating plate for the brooder. I think she is rubbing her wings on it.
Hi @Quik1th Welcome To BYC. It looks like the OP has not been online since April 2017.
I can only assume by the last comment she made, that the chick was rubbing off the feathers/formed calluses by pressing them against the plate.
Do you notice any rough spots in the coating or even hot spots on the plate that could cause this?