P: Noise reduction effect not displayed in Develop mode

Disabling GPU acceleration solve the problem for me (GT650m). Not sure about performance changes. My files already edited in LR6 have this issue, but think I'm did't exported they before. 
Trying to update macOS for latest version and test.

The issue seems to happen with files I edit after updating to LRCCC. Meaning my older files, which I have already edited dont have this issue. Its only on files I havent edited before. Looks like a driver issue to me...or driver-lightroom compatibility issue.

It's good to see that I'm not the only one having this bug. I have a GTX 850m and the bug disappears when I turn the GPU acceleration off. I hope Adobe adresses this issue ASAP, because I really feel a drop in performance when I'm not using hardware acceleration... And it's pretty clear that this is not a graphics card driver issue, since there was no bug when using the older versions of Lighroom.

I updated the GPU drivers from 385 something to 387.92 but no luck

I was just on tech support with adobe and the guy said my GPU was outdated (LOL) he said to wait for a GPU firmware update. LRCCC requires directx 12 or Opengl 3.3. My GPU supports both

Id go more for LR bug than driver issue.  Ive just tried it on older drivers as well.
Performance doesn't seem and different at all with GPU acceleration turned off so for now i guess i'll have to leave it off to avoid losing this very very useful feature.

OK im seeing the GPU thing as well. So it must be a driver compatibility issue with the new LRCCC. Im using a GTX titan

Ive found a non ideal workaround.  I've disabled the "Use GPU" in the menu and restarted lightroom.  Without using GPU acceleration normal behaviour is restored, it renders NR and Sharpening in fit and fill views.  Re-enabling GPU functions and it stops again.
FWIW im on Windows 10 autumn update, GeForce 1060 with latest drivers.

Maybe someone else experiencing this issue can test with and without GPU acceleration and a LR restart.

Its an approximation that is accurate, gives a good general feel of the image and something lightroom has done for years.

Here are some pics. Hopefully the differences are visible on the screenshots
 
Image 1: NR-0 and WB-auto


Image 2: NR-100 and WB-auto


Image 3: NR-0 and WB-As Shot


Image 4: NR-100 and WB-As Shot