Some icons in workspace just dissapeared and now shown as a black square.
Tried to reboot, PHPed update to current version and deleted Windows 10 icon cache. No success.



Explorer shows the icons:

This is not icon cache. You have a problem with one of shell extensions.
Utilities like tortoise-git, tortoise-svn etc register DLL with shell so it can alter icons displayed in Explorer. They can add overlays, for example.
Looks like one of the DLLs is broken and it's hard to tell which one until you uninstall corresponding product(s) and re-boot.

Noticed the same thing a couple weeks ago but did not think about recent installs being the culprit until reading Dmitri's response below.

I had installed OBS Studio to do screen captures.

Uninstalled OBS and the PhpEd JS and CSS icons came back.

LarryG