Bald spots can be from a number of things:
Over-mating from roosters which will generally be on the back
Random spots everywhere or on the back of the head from other hens pecking
You have a broody hen that wants to line a nest with feathers
Mites and lice
Not enough nesting boxes
Attempting to force more eggs with too much light
If you have questions about which it might be, email and I’ll be happy to help you make the determination.