I just recently ran into this same problem, the thread that I had started can be found here:
http://archicad-talk.graphisoft.com/viewtopic.php?t=10399
From what I gather from searching the forum, only team leaders can create views and what causes them to disappear from time to time is the team leader changing from different users. There are some workarounds that I've found on the forums but nothing that would permanently fix this. Its been the same for me, sections and elevations disappear.
RA 2012 x64, Piranesi 6 Pro, Sketchup 8, Windows 7 Pro x64, Intel Core i7, 10GB RAM, ATI Radeon Mobile 5870