Lightroom Classic : Some (Many) Thumbnails are Missing from Grid View

[tleetabor]

My catalog is fairly large, I believe; total ~8200, and is separated into many folders by year. Within the "year" folders, there are nested "day" and or "event" folders. Many, but not all, thumbnail previews do not show when selecting folders, or in the filtered view. If I click and "rest" on a photo, after 4 to 20 seconds, then clicking away, the preview eventually shows. Of course with ~8200 photos, and I'm guessing several hunderds - maybe a few thousand - of them not showing a preview, the time consumed with the rest/click away technique is exhorbitant. And I'm not sure the thumbnails are persistent for future visits, as I've been struggling with this issue for months. I've tried many "answers" that I've found on the internet without anything really  solving the problem. Amongst other "fixes" I've done the select all>library>previews>build standard-sized previews several times, and other than adobe consuming high %'s of CPU for several minutes, I have not noticed any previews actually generated.

What do I need to do to get my previews back to the way they used to be only a few months ago? I'm at my wits end!

See attached photo for what I am seeing (and am sick and tired of seeing!!!). Thanks in advance for your recommendations!

[Rob_Cullen]

~8200 photos in a catalog is tiny/ miniscule!  1 million is 'large'. (Mine is ~65,000)

You have three 'Operations' running-

Are all those processes re-building thumbnails? (Which you might have done multiple times)

Do you have the Preference option to [Save metadata to files] automatically? (This will also take 'time'.)

The badges on thumbnails suggest that previews are re-building-

You might find some useful information in this link- Performance - The Complete Series on Optimizing Lightroom's Speed | The Lightroom Queen 

[tleetabor]

I think 2 of the 3 operations in progress were re-building thumbnails (can't remember the other). But at the time of the screen shot, they had been "in progress" for several minutes (30?) with no signs of progress. Thanks for the note regarding the checking previews sign, and I will check out the performance link you gave!

[tleetabor]

... and BTW, where I see the three dots, if I click on the blamk thumbnail, then click away from it (usually another blank thumbnail), after a few seconds, the thumbnail shows up. But it never seems to show up until I do that click/click away operation. And obviously, that is not practical for thousands of pictures, much less ~65000!

[Rob_Cullen]

This link PREVIEW CACHE ERRORS  mentions grey thumbnails. And it might be worth trying a full deletion of the {......previews.LRDATA} folder. It will mean that previews still need to be re-built (as you have already tried from the menus), but a 'clean' previews cache might help the re-build. It is a slow process, expecially for large catalogs!  Give it more than the "30 minutes".

Other considerations- Is you catalog (and previews cache) on a fast internal drive? Does this drive have >20% free space? Does it have full Read/Write permissions? What is you system information?  From the MENU: Help > Systen Info...   Post a screen-shot.

[GoldingD]

Deleted, my bad, reply in wrong post.