June 2019 - last edited June 2019
If you are trying to demolish the house through the House Options menu and there is no Sim on the lot either living there or visiting, and it still does not work, then you need to contact support at this link: https://help.firemonkeys.com.au/hc/en-us/requests/new
July 2021
The game can't save anything to the cloud while your sims making a "visiting" tasks. I think it's related somehow. when I brought back my visitor from a friend the lot become available to demolish.