I am able to check the "Show all floors" box. And it does what it should. No problems. But whenever I click on "Add floor" or the menu to change to another floor, that whole tab/menu bit just disappears and nothing else happens. It comes back when I switch to another mode (2D/3D/Roam), but again if I try to add a floor or change to another floor it disappears. 

This problem is huge because I am completely unable to progress any of my projects on any other floor but whichever the project happened to be on before this started. This problem occurs in every single project I have. This started sudenly. Everything was just fine earlier today. 

Has anyone had this problem before? Is there anything I can do?

I've already tried:
- Closing and re-opening the project(s).
- Completely clearing all my browser data and then signing back in here.
- Completely clearing all my browser data, rebooting my PC, and then signing back in here.

Nothing has helped at all.