Generic app icons showing

I've noticed that many of my application icons in the applications folder are displayed with a generic icon (shown below). What's weird is that It seems random. Some native apps and 3rd party apps have the generic icon. If I view the applications folder from finder the icons are shown differently than viewing them from the dock. If I highlight an app in finder, the preview on the right may or may not show the correct icon. Sometimes it will show the app icon, but then suddenly switch the the generic icon, and vice versa. When I open the 'affected' apps sometimes the app icon is shown correctly in the dock. But not always. A couple of times, when I try opening the app, it gave me the message below. But then I tried opening it again, and it opened.

Strange things a happenin'. Ain't no doubt about that. I believe it started after the Security Update 2017-001, but I cannot recall for sure.

I've tried restarting the dock, finder and the computer with no luck.

Specs:

(500GB storage, ~100GB free)