CORRECT SOLUTION: The thing is that there’s still a redirector inside the folder that doesn’t get deleted.
show redirectors in content browser (optional): Click on the content menus filter drop down box and enable displaying redirectors (i think you’ll find that at the bottom somewhere probably the last option).
fix up redirectors: in UE content browser right click the folder that can’t get deleted and click on “fix up redirectors in folder”. This will get all redirectors worked out and when it’s done, you should have no issues deleting the folder.
DO NOT JUST DELETE THE FILES IN THE OS FILE BROWSER