I used a mod in my game for a while which just placed one container in Novac, I found this was causing sections of land to disappear when first visiting an exterior cell. I want to start seriously modding myself but I want to know if this sort of thing is common and can it be avoided at all.
This issue is not a common side affect of simply adding an item or object to an exterior cell. Without seeing the mod, knowing what it's true intent was, I could only guess that it had some more serious glitches but, that is only a guess. There are other factors which can cause similar problems, such as too many mods in your load order for example.
My point being, you shouldn't expect to run into missing landscapes if you add items to a cell or, worldspace. If you have over 150 mods running at a time, ( the new "Low Limit" from what I've read but, again I could be wrong. I've never gotten near this number of mods myself!) you should expect to see things like this issue. To many mods at the same time will also cause odd glitches.
cev
P.S. I'm not saying I'm an expert on how many mods can be run before you'll start to see strange issues. I'm only speaking from the point of view of what I've read on some threads and, again, have never tested this limit myself. If I'm wrong (anyone,) please correct me! I would like some conformation on this subject.