I have tried several of the things posted here to fix the screensaver not activating issue but none of them kept it working. I finally gave up trying to fix it and instead just use PowerShell. I open a PowerShell ISE window and use the script below. You can adjust the time you want to use. I generally just leave this running but when I'm using the laptop for a long time I just stop the script.
While ($true) {
Start-Sleep -s 600 #10 minutes
[String]$DefaultScreenSaver = (Get-ItemProperty ‘HKCU:Control Panel\Desktop’).{SCRNSAVE.EXE}
if ($DefaultScreenSaver) {
& $DefaultScreenSaver
}
}