My catalog shows 2k+ images labelled "Photos That Failed To Build a Smart Preview" however when I create Smart Previews of these images they do not get removed from this set nor does the quantity of photos decline.
Screen grab shows an example. Any suggestions for a fix are welcome.
LR sometimes soils its preferences file, and resetting it can fix all sorts of wonky behavior. That article explains how to restore the old preferences if resetting doesn't help.
2. Use the free trial of the Any Filter plugin to see what the catalog internally reports for the presence of the smart previews. Select the built-in collection Photos That Failed To Build A Smart Preview, run the Any Filter > Filter command, click the magnifying glass, and select the Has Smart Preview criterion:
If Any Filter reports that all those photos in fact have smart previews, then the problem is just that the built-in collection isn't getting updated. But if Any Filter reports that those photos don't have smart previews, then the problem is more serious.
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This error is coming from LR internals, not the Any Filter plugin itself, strongly suggesting a catalog inconsistency. It's tempting to ignore inconsistencies, but that portends danger down the road.
I've never seen that special collection, Photos That Failed To Build A Smart Preview. I tried to provoke it by changing the permissions on the catalog subfolder "<catalog> Smart Previews.lrdata". LR then displays an error dialog when it fails to build smart previews, but it doesn't create that special collection.
It may be that this special collection is used so infrequently that's it's never been thoroughly tested by Adobe, and the problem could be simply in how that collection is built and accessed by LR, not affecting the rest of the catalog.
You could try Johan's suggestion of exiting LR, moving "<catalog> Smart Previews.lrdata" out of the catalog folder, restarting LR, selecting the special collection, and then doing Library > Previews > Build Smart Previews. If the special collection goes away, then I think you can rest easy. If it doesn't...
p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post if it helps you get responses.