vlc8uo wrote: This never happened with earlier versions of Photos. I really hope someone at Apple or in the wild can provide a solution.
The thing is, I too have multiple folders and sub-folders, but it still doesn't happen to me (except for that 1 nomadic Smart Folder!) So what's the difference? I imagine that you have restarted you computer-- always the first thing we try.
Have you tried rebuilding your Library? Close Photos and re-launch by "option-command-clicking" the app icon, and telling the pop-up dialog to repair. It may take a few minutes. As always, it's good to have a backup of the Library before doing something like this. If you use iCloud to synchronize Photos on your devices, this may confuse it for awhile. I would disconnect the Library from iCloud before messing around with it.
What happens when you're using another Library? Do the folders still wander around? If you don't have another Library, you can make one by closing Photos and then option-clicking on the Photos icon. Then import a bunch of pictures to it and make some folders and albums. See if the problem recurs with this new library.
I would try making another account, and then opening the problem Library as this new user.
It's always worthwhile to re-start the computer in Safe Mode. This bypasses certain potentially disruptive processes. Safe Mode is different for different computers, so see this:
Start up your Mac in safe mode - Apple Support
The idea is to find out if the problem is with the Library, with your account, or with caches and login items, or even one or two pictures that are corrupted-- stuff like that. One of these steps may fix the problem, but their failure to work is also diagnostic.
By the way-- is your Photos Library in the Pictures folder on your Mac, or is it on an external drive. If it's on an external drive, there are a couple of things to watch out for, like formatting, Time Machine, and ownership.
Move your Photos library to save space on your Mac - Apple Support