First thing I’d try is in the plan, right click anywhere on the floor and choose Display Settings -> then Hidden Items. Is there anything listed? If so, choose Select All, ->then choose Display (lower right), then OK. That will make them appear on the plan, and you can delete them.
If there is nothing there, try grabbing the floating things *while* you’re in Room Viewer – you should be able to right click them – then choose delete.
Ariana