Lightroom Previews Disappear

I have had this issue since Lightroom 13.5 and was hoping it would eventually get fixed but it still hasn’t.

On a Mac Studio M1 Ultra (MacOS 26.5.2 but it has happened on OS 15 onwards) when using “Export As Catalog” where I select “Include available previews” and export a relatively large amount of photos, the parent catalog will lose all of its previews requiring a deletion and regeneration of all standard previews.

The exact number of photos being exported that causes the issue is hard to pin down but over 25,000-30,000 will almost always cause it. I can also make the issue appear by exporting a bunch of small catalogs that eventually total up to a larger number of photos (ie. exporting 4 catalogs of 6000 photos).

During the export of the catalog, I will know the bug has occurred because it will skip the “copying previews” step of the “export as catalog” process. The new child catalog will not have any previews in it.

After this glitch occurs, the parent catalog will sometimes show no previews (just grey boxes for the thumbnails of photos). Other times there is no immediate consequences in the parent catalog. However in all cases, upon closing and re-opening of LrC there will no longer be previews for any photos in the catalog and they all need to regenerated.

This issue has occurred for two years now. It happens on brand new fresh catalogs (with a sufficient number of photos) and older catalogs that I have used for a long time.

Attached is a video of the bug happening.