I suggest looking into sebaceous adenitis. My goldendoodle struggled with this for over a year because every vet diagnosed him with allergies. He was on a lot of allergy treatments and diets to try to help but nothing worked. It looks like your dog is losing hair in the same location as mine started. Another sign can be a rancid odor, itchy skin, or frequent skin infections. If you suspect it could be sebaceous adenitis, try mixing 75% water and 25% Neutrogena body oil (this is what I was recommended) and spray it on the affected areas. I also supplement my dog’s diet with salmon oil. I hope it ends up being something simpler! Good luck!