I notice one of my 18-month old barred rocks having the same bald area. Seems getting worse. And her poop is brown squishy. Appreciated if you suggest how I should address it.The spray won't hurt if she doesn't have it.
You can try some vaseline. I think it will merely be a dirt attracter, though.
It could be some simple loss of feathers that is harmless. We can hope.
LofMc