For some reason, I have a specific spot inside one of my ADTs where I cannot select objects anymore unless I look at them at a specific angle and click them in a specific fashion. I also seem to be unable to edit the terrain or heightmap in this location unless I'm sneaky about it. (This is a Blizzard location btw)

I tried the "Clear Models" function just to see what would happen, and it deletes everything except for ONE object. The object that doesn't get deleted seems to change every time I use this function. Not sure what that's all about but whatever; I don't think it's that important.

Using the "Clear Models" option fixes my problem. I am once again able to place/select objects and edit the area around/within. However, I obviously don't wanna delete the entire town I just built, so I'm not very inclined to using this solution. I was wondering if anyone else had a better idea to fix this problem, and it would also be very helpful to know why this problem occurred in the first place. Please and thank you.