Black screen exiting game

@Malkus74 interesting issue you have but no fun to fix. I have a win10 enterprise on a spare SSD I play with when bored to see how well I can lock it down and turn off the big brother spy crap in win10 lol. Anyway one thing I did learn in win10 is it has mega issues still with more then 1 screen as the rig I test win10 on is connected to 3 screens all the same. What went down for me was the screen resolution on 1 or 2 screens went way small could not fix it.....the fix was turn off PC unplug screens from PC and wall for 1 min plug them back in and boot up and fixed. 

With your issue I am thinking like you this is due to 2 different screens with 2 different connections :/ Just for testing on this I would remove the dell screen and see if you get the same issue after a game. If you have not tried this already. All 3 of my screens are the same and connected with DP cables and win10 gave my 3 screens issues. So  my gut says this is a win 10 issue due to 2 different screens with 2 different connections. In the weeks I have spent testing and playing in win10 this OS is not fully stable or fully good to go yet and this is why I test on a spare SSD so I do not have to reinstall win8.1 when fed up lol.