In my case it helps to restart the service lightdm (sudo service lightdm restart) - this works around 50% of the time, but in some cases the system freezes afterwards and a hard reset has to be performed.
Another issue is that if the second monitor goes to sleep it is not waking up afterwards. -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to xorg in Ubuntu. https://bugs.launchpad.net/bugs/1574005 Title: HDMI connection not working on Ubuntu 16.04 and GeForce GTX 960M Status in xorg package in Ubuntu: Incomplete Bug description: The bug is described in question #291879 . After upgrading to Ubuntu 16.04 the HDMI monitor is no longer detected. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1574005/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp