Develop module grey screen on some images using backslash

[johnw7182060]

in Loupe View I usually hit the backslash (\) when I want to see before image in Develop module. Now often I just get grey for Before image. If I use the YY it displays both the Before and the After image instantly. Have deselected Use Graphics Processor and the same thing happens. Some developed images are fine, sometimes it changes the view quickly, sometimes it takes several seconds, sometimes it never loads the Before but I can see the little grey outline where the Before frame is. If I hit the Zoom tool (inside the grey Before image, the + in a magnifying glass Icon) it brings up the Before. Sometimes I have to hit the Zoom several times before I get the Before image. Memory usage is about 65% (have 16GB RAM), CPU about 5%. Sometimes when I use the Graduated Filter it reacts very slowly as well.

Thanks

[Per Berntsen]

This is probably caused by a defective or incompatible monitor profile.

Try setting it to sRGB, use Adobe RGB if you have a wide gamut monitor.

Restart Lightroom to make it aware of the new profile.

See How do I change my monitor profile to check whether it’s corrupted?

If that fixes the issue, you should ideally calibrate your monitor with a hardware calibrator, which will create and install a custom monitor profile that accurately describes your monitor.

Another possibility is that your Develop previews are corrupted. These previews reside in the Camera raw cache.

Go to Preferences > Performance, and click Purge cache next to Camera raw cache settings, this will delete the previews.

[johnw7182060]

Have a top level Dell 4k (P2715Q) monitor professionaly calibrated, also have purged the cashe. The monitor and program have been working perfectly for a long time. Today was the first time I've had the problem. Have closed the program, rebooted the system.

[Per Berntsen]

I suggest that you try setting the monitor profile to sRGB.

Monitor profiles can become corrupted, you may have calibrated using incompatible settings, or a Windows update has installed a bad monitor profile. (I'm guessing you're on Windows)

[johnw7182060]

monitor profile is sRGB. I don't think global monitor settings are the problem. The only time there is any problem is in the Before window in Develop module, everything else in LR and other programs looks great. I think it is/was a glitch in LR. I'm editing large files from a Nikon D 850. This evening it is working OK, for now.