@Heidi675 We had a set of guests once who took 3 comforters out of the linen closet and used them, along with the bedding that was already on the bed. We could not believe it.
After that we put a typed note in the linen closet stating that if guests require any different bedding to please contact the hosts.
I would probably message those guests and ask them the reason why they took an additional set of bedding out of the closet. They may not respond, but they might and that would give a clue what the reasoning was.
@Mike-And-Jane0 We always washed the comforters after every guest, but since comforters are not really meant to be washed/cleaned very often, and queen or king sized comforters can only go in commercial machines...the cost was high and they were getting destroyed by all the washing. We switched to quilts. It isn't as luxurious looking as a comforter, but easier to manage.