There is a posterization issue with the camera matching profiles that Lightroom has for the D810. This could well be it. AFAIK there is no update for those yet. Try a different camera profile such as Adobe Standard. If that fixes the posterization than it is this issue and you'll have to wait until the next Lightroom update to get updated profiles (hopefully).
>Can this be due to active d-lightning without lightroom knowing about it?
No, but it is advisable to not use any modes like this in camera when you use Lightroom or any other non-Nikon raw software because all that the camera does to the raw is to underexpose it and save an instruction to apply a HDR treatment in Nikon's raw software. Other software won't be able to read that instruction and it will make the images appear underexposed as they actually are.
OK, thanks! Switching to portrait solves the problem. Thanks again!
Adobe has a Help page where you can download beta profiles that fix the issue. Of course the profiles would need to be updated to the non-beta versions when the next version of ACR and LR come out so I would use them sparingly and add a keyword or something to each image you use them on so you can identify them, later, to switch the profiles to the production version.