Been having this problem since day one with our ineisis integration but with the increase in traffic on our server, it seems like people are reporting more and more of these mysterious holes cropping up every day. They don't disappear to so if something isn't resolved we're going to have a serious problem on our hands.

I equipped the foliage tool to show that it slopes up as you would expect it would if the terrain were still there, so apparently some level of the engine knows what should be there, but other than the way the tool responds you still just fall right through it.

It seems to be completely random when they appear as to both the size and location. They happen randomly throughout the game world and never really disappear.