Nicinus

Most likely you have an issue with your hole in the floor platform above. Did you create a hole with the Auto stairwell tool or used railings? If railings check that they close properly, use an opening instead of a gap, and finally make sure that the room on the second floor is defined as open below.

I had some different things in combination that confused me, but the main thing was apparently that I was dimensioning through a doorway.
 
I wanted the extension lines to go to the jamb, but the dimension saw the doorway as a sold wall and therefore no need for extension lines.

Old topic now, but for those that search for it I've found the following:
 
1) Sometimes when I use the middle mouse to pan in the 3D window, I accidentally press the MMB sideways and the geometry scoots away for me. I now know when this happens and a couple of taps in the other direction brings it back. Initially I tried to recover by using zooms and dolly, which generated massive distortion and consequently not a good idea.
 
2) The view can be reset with '3D/View Direction/Restore Original View"

When I created the roof I was standing on the first floor, and when I changed to the second and recreated the roof it worked as expected.