Comment 73 for bug 1295267

Here's my 5 cents.

( tl;dr - use gnome and gdm )

I've been running Ubuntu 16.04.2 for long time on Dell Latitude E7250 without any problems using Gnome.
I have two DELL external monitors, one connected with HDMI straight to laptop and the other connected with DisplayPort to the docking station. HDMI connected monitor is pivoted.

Last week my laptop came for IT suppport after reinstallation of Ubuntu due to some other reasons.
Now the desktop manager was Unity.
When locking screen and automatic screen off, my system froze completely.
I changed back to Gnome. Still same effect. Then I changed also from lightdm to gdm.
-> setup is the same as before the reinstallation -> no problems any more with screen locking.