This issue has been around since Cubase 7 or so, and it has still not been fixed. I figured this would be fixed eventually, but I guess it needs an issue report to get some attention.
To reproduce, start Cubase and let it load. Switch to another app, like Chrome, then when Cubase finished loading, click on the Cubase taskbar button, it will just blink and Cubase will stay in the background. I always have to minimize all other windows to access Cubase… Please fix this, because it is getting pretty annoying.