For the past week or so, I've been unable to use the @ mention system in the old UI. Nothing pops up when I try to use it.

The only workaround I've found is to use the editor in the new UI, where it still works perfectly fine. As someone who prefers the old UI for articles, I'd prefer not having to switch between them constantly just to mention other articles within articles.

I've deleted all my browser cache and done everything the list said to try, but it's still not working. It does it in any article I try to edit on the old UI.

Go into any article in the Old version of the editor, go into any text field, type the @ symbol and at least three characters, and no UI window for article selection comes up.