Using keywords in Smart Album

That suggests to me that there is one or other of the keywords in the main library that's triggering the crash. Using the Keyword Manager (Window -> Keyword Manager -> Edit Keywords), inspect the keywords keeping an eye out for odd diacritical marks or symbols. If you find one, remove it and try again.

I'd go ahead and rebuild the Library-- see below.

I usually follow these steps in order to narrow things down,

• Restart the computer (of course)
• 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 

• You did this one: 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.
• Rebuild your Photos Library--close Photos and re-launch by option-command-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.
• 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 move your Library out of your own user's 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…

For what it's worth, that's not happening here.

Try create a new library as a test, add a couple of photos and see does the problem recur there.