This is a very frustrating "BUG" in ACAD15 concerning Interior Elevation's linked to Zones. Every time I close and re-open a BIM 15 Project all my interior Elevation numbering disappears.
You then have to modify the perimeter of that room Interior Elevation (on each room) or the zone perimeter, to get it back:
Graphisoft has told me that it is project related, so I packaged it and sent it to them... had no response yet! This happens to me when I turn a normal project into a BIM Teamwork project. I will try and save it as a normal project again...
sometimes changing one zone and then using the "Update Zone" brings back the names
... Frustrating!!!