Pretty crazy! You haven't said if your are using iCloud Photos. If so, do you use Optimize Storage?
Do you use a VPN? How about Mac "Cleaners" or "Virus Catchers?" These are all known to interfere with database operations on the Mac, and they have also been found to corrupt Photos Libraries. If you have any of these things, you should remove them from your computer.
After that, try these things:
1) Restart the computer (of course)
2) Re-start in Safe Mode. This bypasses certain potentially disruptive processes, and it often helps. Safe Mode is different for different computers, so see this:
Start up your Mac in safe mode - Apple Support
3) Rebuild your Photos Library--close Photos and re-launch by option-command-double-clicking the app icon. If you use iCloud Photos, it’s possible that this will cause a re-sync that lasts long enough to make you nervous. I usually turn off wifi when I do this.
4) Use another library if you have one, or make a small test Library with a few pictures in it and see if the same thing happens. You can create a new Library by closing Photos and then option-clicking on the Photos icon. If you use iCloud Photos, that won't connect with this new Library. You can return to the original Library by using the option-click method above.
5) Make a new user and see if the same problem recurs with it. This is a bit harder, because a new user can't access a different user's stuff. You would need to temporarily move your Library out of your own user's Pictures folder up to the general "Users" folder.
The idea is to find out if the problem is with the Library, with your account, or with caches and login items, and stuff like that. One of these steps may fix the problem, but their failure to work also helps figure out what's happening.
Let us know what happens…