Lost images in collection

I suspect they are no longer on your computers hard drive. Look in the FOLDER they are supposed to be in and see if they are visible.

It looks like you have a lot of collections. You may have it a wall with the number of collections allowed. Not sure on that but I think I read about it before.

Try optimising the catalogue.
Also, in the last few versions Adobe has been doing work to cache the folder/collection counts and I've sometimes seen them getting stuck. Try adding a photo to that collection and see if that frees things up.

I’ve exported the collection as catalog and it contains images. They’ve been merged into a panorama and stacked together. That’s maybe a beginning of explanation...

It appears that LR's filters are in an inconsistent state -- the upper-right corner indicates a filter preset has been applied:



(If only more people would post full-resolution screenshots.)

I've seen this happen a number of times over the years.  Two things to try to correct this:

- Click the preset menu and click Restore Default Presets. Then click the preset menu and select Filters Off:



This will restore the definitions of the built-in default presets (which can get corrupted or accidentally updated) but not affect your own presets.

- Reset LR's preferences: https://www.lightroomqueen.com/articles-page/how-do-i-reset-lightrooms-preferences/. LR not infrequently soils its preferences, which can cause screwy behavior in the application. 

Please be sure to save a copy of the preferences file before you reset them. Then we can send it to Adobe to do a post-mortem on the corpse.  In the past year, they've made noises about wanting to track down the cause(s) of preference corruption, though I haven't heard much recently.

"Resetting the default presets was a good idea, even though the filters were already off. It didn't help, even with "Filters Off selected", as in you're screenshot. Furthermore, I now end up with duplicate presets. No big deal; I almost never use those presets."

Hmm, this indicates that your LR remains very confused about filters.  One more thing to try:

- Go to Preferences > Presets and click Show All Other Presets, which will open Finder / File Explorer on the LR presets folder.

- In the "Filter Presets" subfolder, move all .lrtemplate files out of that folder into some other location (e.g. a temp folder on your desktop).

- Restart LR.

- Click the preset menu and do Restore Default Presets.

- Restart LR.

- Click the preset menu and do Filters Off.

Hmm, I have a vague memory of someone reporting similar symptoms with stacking in the last couple of years, but there's no way I'd be able to find the post (and it might have been discarded by Adobe if it was in the user-to-user forum).

Normally stacks in folders and in collections are totally separate, and stacking in folders isn't viewable within collections and vice versa (LR's stacking rules are exceedingly complicated).  So in theory, the stacking in your folder shouldn't affect the collection. 

But you could try this:

- Select All Photographs and do Photo > Stacking > Expand All Stacks.

- Select the collection and do Photo > Stacking > Expanbd All Stacks.

I'm skeptical, but you never know...there's clearly something screwing about LR's filtering.