Really. Apple Photos has been a dumpster fire for my wife. It randomly freezes, she can’t get her photos back out to upload them, etc. It’s almost to the point that she’s done with MacOS because of it.
Is your photo library on a spinning hard drive or USB drive? I had this problem before which the setup, and it went away when I moved my library to my internal SSD.
The good old "if it's not working it's because you're not using enough of it" ;)
Moving it becomes necessary when you acquire lots of photos and videos
A decade plus library of photos & videos here; probably in the 50k mark now, it’s been pretty flawless for me other than than the iPhoto to Photos upgrade. Never really had any issues with imports and exports (which is how I ended up upgrading). I’ve even used the iCloud sharing more often than not which has been a bit clunky but works once you figure out how to get a link out to people.