Actually, it's a bit of a rabbit hole, but here goes:
Firstly, the issue of posterization in D810 files was an Adobe issue. Lightroom v5.6 included the D810 as a supported camera. But the developed images had posterization for all users, due to a problem with the Adobe built camera calibration files for the D810. Adobe then published beta camera profiles that corrected the problem and those corrected profiles were included in v5.7. That seems to have fixed the problem.........no further complaints except for me, where the problem still persists still with v5.7
With that background, my Q was framed around whether or not Win updates (way too frequent......what? Once a week or so?) might be the cause of this posterization still present on my system despite upgrading to v5.7. IOW, the Q was: Do Win updates cause problems for LR software? At this point, I'm searching for possible causes. You and DdeGannes indicated that Mac is more problematic.
Secondly, inasmuch as it appears to be software based, I would hope that this posterization issue (although fixed for others) is confined to LR. I've heard of no one complaining about this D810 issue with ACDsee or Capture One Pro 8. I've checked both user's forums dating back to the intro date of the D810. Zero comments or complaints about the D810 files and the respective software.
I'll know the truth tomorrow when I pick up the cleanly rebuilt (software-wise) Asus Laptop.
I'll report the results here as to whether or not the OS (maybe?) or LR (maybe?) was corrupt in some way. Maybe one or the other or both, or none. I understand I won't be able to discern which one it was, if either at all. I'll still report back with a description of how the machine and LR are doing.