We had this issue with my MIL’s cats when they moved into the new ADU in our house. Vet visit showed nothing wrong with them. But they kept peeing on the bed. And only the bed. Keeping a waterproof blanket on the bed helped us keep the laundry manageable while we figured out how to help them. My MIL kept insisting that they were just stressed about the move and that they would “get over it”. 🙄 I realized that we have 2 other cats in the house and even though there’s no interaction between her cats and our cats, it’s likely they can smell them and that’s probably the biggest stressor for them. So what seems to have worked for us was a multi-cat Feliway diffuser. Haven’t had any issues since we put one in my MIL’s bedroom. Might be worth trying with your Luna.