How do I restore the icons of the Dock's Applications folder? For some reason, many of the applications' icons in the Dock's Applications folder were replaced by the default application icon. I've tried to clear the icon cache, but that didn't work. Below is a screenshot of the problem.

How do I restore those icons? And for that matter, why did this happen in the first place?

I'm running MacOS Sierra on a MacBook Pro Mid 2014.
Well, I restarted and did a first aid on the volume, and now it's working. I don't know what did it, the restart or the first aid, but it's working now.