Never had this problem seen before in all my years of LR use. I use a test-chart with a continuous gray bar (from dark to light). Normally use Camera Standard profile to develop all my D800 RAW files with no problem so far. Got a D810 to test this week and did some tests using the same target. Suddenly there are some ugly posterization effects in the gray bar to be seen that can only be eliminated with heavy color-noise reduction or by switching to any other profile but Camera standard, Camera Vivid, Camera monochome.
The following 100% crop shows the effect from a D810:
And this is the same crop from a D800-shot: