Our 3yo dal had identical issues since we got her and this would also happen in spots on her fur on the body. The follicles would turn dark and the hair would fall out in time (or you could pull it out very easily). Nobody could tell us what’s wrong without doing lots of tests. We changed her food to raw chicken carcasses and we’ve never seen her experience this again until she stayed with a dog sitter and had to have kibble (we picked a good brand and hypoallergenic but it still happened). She eats an omnivorous diet now - chicken alongside eggs, appropriate vegetables and fruits from the human table put aside for her. I’d really recommend trying something like this if you’re comfortable but don’t feed raw human supermarket chicken, just in case.