See a vet, get their opinion. However, I will say we had a cat who developed some hair loss in a few places here and there. One of the vets insisted it was probably fleas, recommended treatment and all that. We knew we didn’t have a flea problem. The hair eventually came back. We’re pretty sure some dynamics in the house going on were causing them to be nervous and either scratch (hives?) or just lose hair as a reaction. And that kind of thing is hard to diagnose from just a single vet visit.

But see a vet, maybe it’s some skin condition or something else they can see the cause of. Perhaps diet change? Allergy to something new, or got into something? Lots of causes.