A resource mailbox is set up to schedule meeting rooms, or other resources like projectors, laptops, etc. The auto-accept is used for those and works properly when the resource mailbox is included in the invite as a resource, not an attendee. It is supposed to work as a booking process. If users invite a resource as an attendee instead of a resource, the invite will stay in the inbox and not be processed just as you describe. It is working as intended. If people are booking YOU as a “resource” that is not going to work very effectively. You need to create a resource mailbox separate from yours if you want it to work this way.