Disappearing fotos from Album in lightroom CC

Generally speaking, photos don't disappear from the cloud without some form of user action, which may often be unintentional as understanding the sync/delete process can be confusing. If I explain how it is designed to work, maybe you can try to match the "rules" to some form of inadvertent action on your part. The key may be in your comment that you had "synced to desktop", but it isn't clear from that comment if you mean that you synced to the desktop LRCC app, or to the LR Classic app.

Leaving Classic aside for now, all photos in the cloud are available on all synced devices that use the LRCC app, be that on phone or tablet, or web browser, or desktop. In all those apps the photos appear under the "All Photos" section, and may additionally be organised into albums. So a synced photo can exist in any number of albums, or no albums. If you delete an album from any of the synced devices, that album will be removed from the cloud and thus all other synced devices, but the photos themselves are NOT deleted from the cloud or other synced devices, i.e they are still available in the All Photos section.

You can also remove individual images from albums, that removal syncs to all other synced devices, but again the images will remain in the cloud system in the All Photos section.

You can also delete individual images, either via an album or All Photos, and that will delete the images from the cloud and thus all synced devices.

All that is fairly straightforward and there are suitable warning messages issued where appropriate. However, things get a bit more complicated when you enable sync in a Lightroom Classic catalog. When that is done you can sync collections to the cloud (only Smart Previews are uploaded), and those collections will appear as albums in the cloud and all LRCC apps. Similarly, any existing images and albums in the cloud will sync down into Classic (in this case full originals are downloaded). In the Classic catalog you will see an "All Synced Photographs" special collection appear in the Catalog Panel in the Library module, and this equates to "All Photos" in the LRCC apps. Again, like LRCC, photos in Classic can be synced, thus appear in All Synced Photographs (ASP), but don't have to be in synced collections.

When syncing is up-to-date, if you do those removals or deletions in LRCC, what happens in Classic is as follows:

• Remove from an album will remove the same image from the corresponding collection in Classic, but the image remains in ASP, i.e. it's still synced.
• Deleting from the cloud will unsync the image from the Classic catalog, i.e. it is removed from the ASP but it remains in the catalog, i.e. it is NOT deleted from Classic.

However, when you take these actions from within Classic, the result is as follows:

• Remove from a collection will remove the same image from the corresponding albums in LRCC, but you will be asked if you want to retain the image in ASP and thus in the cloud. Default is YES but you can override this. If you do override and say "NO", the image will be removed from the ASP (though it remains in the Classic catalog) but as a consequence it will also be removed from the cloud and thus from all synced LRCC devices.
• If you remove an image from the ASP, same result, i.e. it will also be removed from the cloud and thus from all synced LRCC devices.
• Finally, if you remove a synced image from the Classic catalog completely, it will again automatically be removed from the cloud and thus all synced LRCC devices.

The main thing to understand is that if you sync a Classic catalog you cannot have a situation where an image is synced across the cloud ecosystem but is not synced with Classic. All synced images have to additionally exist in the synced Classic catalog, so removing a synced image either from ASP or the catalog itself will consequently remove it from the cloud.

It sounds more complex that it actually is, but it does mean that when syncing using Classic the user has to understand how removals/deletions work across the cloud ecosystem.

So with all that in mind, are you able to figure out what may have caused those albums/images to disappear from the cloud?