P: Slow UI when using Mac and Custom Display Profile

I just tried that, too (turning off one of my 2560x1600 displays). It doesn't make a difference at all in my case. Interesting, isn't it?

What does make a difference in grid view usability on my setup is minimizing the thumbnail size and turning off extras and badges (View > Grid View Style...). Still far from ideal, but definitely better...

Well that's now to be expected (4K being part of the issue). Good to know. Adobe's on top of this, I suspect they have enough info to get it resolved but what we (and of course they) know is that the profile and type of display are part of the cause. 

I wonder if when drives a 4K display at less that this resolution, that clears up the problem? 

Yes, like night and day. I did not bother to physically disconnect but just turned off the 4K monitor and restarted Lightroom (not even a reboot).

Unfortunately, the other monitor is rotated 90 degrees to portrait orientation due to space constraints and basically unworkable without modifying the entire panel. While workspace is still roughly equivalent to that on a 15" laptop screen, the resolution is much lower and I'm working from 1 meter away.  Not a practical solution.

On the other hand, we were able to isolate at least one factor that is hindering the performance - thanks for the suggestion.

Mine is a dual monitor setup, the main is a 4K monitor - NEC PA322UHD

If you unhook the 4K and do nothing more, any difference?

Yes I read that except that I have been working on my catalog the last few weeks, so losing the changes is not an option.

Save those specific image edits in a DNG, you'll retain them. Catalog edits like collections, probably not.

*Kozzi The solution is go back to the older version PRIOR to this bug which Adobe IS working on and does not affect all Macs. Use the Creative Cloud application and select... then ”other version” and back to work until the next release.

Hi Alexander -- Thanks for the response

Yes I read that except that I have been working on my catalog the last few weeks, so losing the changes is not an option.

Switched the color profile to Adobe RGB on both my NEC monitors from icc profiles calibrated with Spectraview II (sRGB? Not even going there).

At least the scrolling performance in Library module has improved, but the same amount of lag when selecting particular image(s). 

Mine is a dual monitor setup, the main is a 4K monitor - NEC PA322UHD - where the main window resides. The second monitor - NECLCD2690WUXi2 - displays secondary display, grid view 99% of the time in both library and develop modules.

Develop module has been relatively unaffected. Dual screen display enables me to keep the grid view open and perform some Library functions that way but switching from one image to another is frustratingly laggy.

In my time owning 2009 Mac Pro that has been upgraded incrementally up to almost its maximum performance capability over the years to keep up with software requirements (and it is still well above the LR hardware requirements), I have never seen so many spinning beachballs - not just in LR but in any software and their applications.

cMP 5.1 running on Mojave 10.14.6

2 x 3.46GHz 6-core Xeon

64GB 1333MHz DDR3 RAM

Radeon RX 580 8GB

Lightroom catalogs are on NVMe in slot 2

*Kozzi Dan, the old Lightroom catalog is still there. The catalog upgrade only occurs to a copy of the catalog. This copy has "-v10" appended to the name.

Your old v9.x catalog is still on your hard drive and you can open it after downgrading. With a few more steps you can also avoid having to rebuild the previews. See here.

Kozzi: now you know what every IT guy knows: don't upgrade until you check! Wait until you get the "all clear" from Jeff Harmon (Photo Taco Podcast) or Victoria Bampton (lightroomqueen.com) that it's OK to upgrade (it's not yet!) For next time? Best advice: get an IT guy to help you!