When I change a folder name from within LR Classic 10.1.1, the folder goes "missing." I believe this is a new problem with 10.1.1. The find-missing-folder feature doesn't work, now, either. To restore the status quo ante, I first restore the original name in the Finder, and then close and reopen LR Classic.
I've seen this happen too. The hiccup is when you change the name you see a question mark... if you then check your folder outside of Lightroom you'll see that the name change is visible. Go back to Lightroom and collapse and reopen the panel and the question mark should be gone. You can also click on another folder and the question mark will go away. It's a quirky little bug for sure.