Since the PBR update, UGC assets that are set up in Roblox Studio as rigid accessories can now be published under layered clothing categories.
For example, a Waist Accessory (rigid) can be published as a Dress Skirt Accessory (layered clothing) because both categories are able to use a WaistCenterAttachment.
We have deployed a fix to prevent rigid Accessories being uploaded to the wrong category. The validation fix has been rolled out on the backend and will also apply in Studio within the next few days. Thanks again for the report!