I have seen this from time to time in animation renders...everything looks dandy in the test frames, then as the shot moves you see a hard linear clip in the Geo, wiping the terrain on or off with a hard line.
Today I'm seeing it in stills from these inverse crater tower things, but only at certain angles.
Here's some fun examples, the RTP grab, and its rendered counterpart.
I realize some of the displacement is wacky, but it doesn't appear to be so far out of school that it cannot be dealt with properly.
I also tried higher and lower gradient patch size settings in the two Compute Terrain nodes in the displacement chain.
Weird? You be the judge!