Photos not showing up anymore in a specific smart album that should show all photos that are not in any album

Hello there.

I had a smart album. Configuration: "Album is not in any". This showed me all photos that are not in any album. Like this I am able to keep a good overview about which photos I have not sorted.

I created a new album and accidentally selected all photos that were in that smart album. This was not my intention so I pressed 'command + z' (reverting the creation of the album).

My expectation: The smart album should show all photos again like it was before the creation of the album. Because now - after the 'command + z' (deleting the album) - the photos are again in no album.

However, the photos are not in the Smart Album anymore. I can still see them when looking at all photos, however like this it is merely impossible for me to sort because I can't say which photos are not in an album already...

Anyone knows what I could do?

I already did a repair of the database from photos which did not help.

Best Regards,

Dave