Images are in the Library, but suddenly missing from many of my collections - since version12 update

In the last few days I have noticed a few images go missing here and there from my Collections. Yesterday, hundreds of photos went missing from a number of collections - in one case from over 400 to zero overnight. Other collections remain unaffected. This follwed the recent major upgrades of Photoshop and Lightroom.

The Library appears unaffected. I am running Mac OS 12.6 and Lightroom 12.

I arranged a phone call from Adobe Support. At the end I was told the application is not at fault, "It's your workflow". I was incredulous. I asked if he thought it was possible I could go from folder to folder, deleting 100s of images, then confirm that I actually wanted to delete them - without any memory of it? He actually asked if I had a screenshot to confirm the photos were there at all!

My faith in the Collections is a bit shaken now. It will be a difficult and slow process to recreate my selections and choices made over years as I rebuild my Collections from my Library.

Am I the only person to experience this? And is there a fix?