I have installed the newest version of Screen Saver 22.214.171.124 in a Win10 v1803 environment.
The File is stored in c:\windows\system32\ScreenSaver_Operations.scr using GPO.
Then I have registry items all configured for Forced logoff. Everything works when I DO NOT have a website running without video -> example www.google.com, in this instance the screen saver.scr window appears and apps like word, excel are logoff properly. BUT when I open youtube and leave video running the screen saver never appears.
I have confirmed that this is related win10 and any video in a browser - does not matter if its Firefox, Chrome, or Edge. If you pause the video the ScreenSaver_Operations.scr works. Please any help would be appreciated.