Although I just noticed this problem in Lr Classic 9, it appears to be present in at least Lr Classic 8.
When I edit a large raw image like a panorama DNG, I am experiencing a significant lag between the White Balance Selector position and the sampling Loupe while moving the Selector around the image when the Dehaze setting is non-zero. Associated with this lag is a complete paralysis of Lr, which goes into a “not responding” state and blacks out the screen for a second or so, then comes back for a short time before going black “not responding” again. It repeats this over and over until I set the white balance with a click or replace the WB Selector on the basic panel.
Here’s an example. I have a wide panorama image open in Develop with no settings applied. I created a new catalogue with only this image for my test. Select the White Balance Selector and move it around the image reasonably quickly. The Loupe follows the eyedropper around the image with barely any lag. I have hovered over the blue sky to make the Navigator preview show a very warm image, as seen in the screen shot below.
Replace the WB Selector on the Basic panel. Change the Dehaze amount from zero to any value, even just +1, as I have in this example. Select the White Balance Selector again and move around the image as before. Now there is a significant lag between the position of the Selector (eyedropper) and the Loupe. The screen may go black while doing this with Lr going into “not responding”. I stop moving the Selector around and hover over the blue sky as before. In the screen shot below you can see the warm image in the Navigator preview.
After a few seconds the screen goes black for a second or so, like the screen shot here.
Lr then recovers back to the normal screen, but then goes black again after a short delay, repeating this sequence until I set the WB or deselect the WB Selector.
The problem seems to be even worse if I have more develop settings, such as, Lens Corrections and Basic adjustments set manually or using Auto, but disappears if the Dehaze amount is set to zero.
I have tried turning off the GPU. This still has the significant Loupe lag while moving the WB Selector around the image and LR occasionally goes into “not responding”, but the screen doesn’t go black, although it might black out a portion of the screen.
I’m running Windows 10 Pro 64 Version 1903 and my GPU is NVIDIA GeForce GT 525M with the latest driver ver 391.35 (only has display support, not develop).
I would be interested to know if anyone else experiences this problem.