Cubase has no sound after playing YouTube

Previously, in Cubase > Studio > Studio Set-up > VST Audio System, I had checked “Release driver when application is in the background”.

I start up my PC, and straight away open Cubase, open a project and play it. No problem with audio. I then open Google Chrome (Cubase in the background) and play a YouTube video. The video has no audio problem either. Then I bring Cubase back to the foreground and play the project again. Now the audio is gone. I check if “Release driver when application is in the background” is still checked. That’s the case.

What’s going on? How can this be fixed?