I was projecting an elevation this morning, then had to change one thing. After that, the elevation came up blank, as did 7 out of 8 of my elevations. Just in case my change was the problem, I got the back-up file from before, which had projected the elevation fine just an hour before, and tried again. Blanks all around, even though it was the unaltered file and should not behave differently.
However, one elevation consistently projected, with no difference in settings that I could detect between those that did not, so the file was capable of producing elevations.
I tried all the usual things, re-starting the server, archiCAD the computer, etc. Even tried on three different machines--no difference.