Photos don't stay cropped

That's weird and, I'm sure, very irritating! I haven't heard of anyone else having that problem. Tell us a couple of things: Are you using iCloud Photos? Where is your Library located-- in you Picture folder, or on an external drive? If an external drive, how is that drive formatted? When you finish cropping a picture, can you export it (FIle>Export>Export nn Photos) to a folder on your desktop? If so, is the exported picture properly cropped?

Try these things:

• Restart the computer (of course)
• Re-start 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 

• Make a new user and see if the same problem recurs with it
• 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.

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.

This is interesting--let us know that stuff I asked, and tell us how it goes...