Update: I had an online chat with Microsoft, and they had me disable all my add-ins. It seems to be okay for now. But it can be okay one minute and broken the next, so I'm not sure if this resolved the issue. We'll see!

What kind of screen shots are you capturing? are they from a locally run program, or do the images come across some sort of remote desktop connection, such as Citrix?

It doesn't matter. Just hit Print Screen and paste into Paint, and then crop and cut/paste into Word. It can be a screen print of anything. I happened to be getting screen shots of Excel (local) this time. Sometimes they were okay, and sometimes not. Sometimes a good image was followed less than a minute later by a bad one. And other times I was copying other software (remote) and it was also randomly okay/not okay. I'm hoping that disabling the add-ons was the fix.