Nicinus's post in Beginner issue - how do I see my stairs on second level? was marked as the answer
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.
Nicinus's post in Dimension Extension Line Trouble was marked as the answer
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.
Nicinus's post in Resetting the camera was marked as the answer
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"