Why can I not move files from one folder to another?

This is really driving me crazy... I try to move items, primarily photos, from one folder to another. Sometimes it's from a folder in iCloud, but other times, it's just moving them into a folder, within the same larger one!

I can move 10 or 20, even 30, then the next time, I get the window that says, "Preparing to move to Xfolder, and under it, "Preparing to move the number of items", like maybe a whole 12 pics. Well, it just stays there, with a line going back & forth, endlessly! If I click on the X, it says "Stopping"... great, but it doesn't stop, just that line bouncing back and forth... The only way to stop it is to FORCE QUIT my Finder, every single time this occurs! Which means if I want to move a few hundred images, (small ones, too), it would take me literally hours, only able to do a few at a time, before force quitting the Finder.

What is going on? This is obviously not how it's supposed to work...