5 month old puppy tries to bite if we take off collar – advice needed

This started a few days ago out of the blue. She doesn’t mind if we take toys or food or treats but for some reason she really doesn’t like her collar being messed with. She’s totally calm if you play with her neck or face or round that area, it’s just the collar she guards. She’s very gentle natured in general so it stands out as weird to us.

She used to have an over the head harness that she didn’t like being taken off so switched to a step in one which she’s fine with but the collar problem remains.

I don’t think it’s resource guarding because she’s totally calm with anything else of hers being taken and never bites or growls but I might be wrong and it might be specifically just the collar she’s guarding?

Any advice would be appreciated