What is this please

[wodin69]

Been getting this on my chicken for about 6 weeks now. It cleans off with warm water and seems to be yellow underneath that goes right into her nostrils.
Sometimes bleeds a little when removed but she seems ok with it. Isn't off her food or exercise.

 

[wodin69]

 

[wodin69]

After removing the top of one of the scabby bumps. It is always a foul smelling soft yellow substance.
We feed her a lot of sweet corn as she loves it best.