Comment 38 for bug 1295267

I have this issue.
16.04LTS - this problem is very frustrating.
Previously, on the same hardware, running 14.04, and then 15.10 I did not have this problem: Display was reasonably stable - "reasonable" not "perfect" because there is a bug affecting HDMI output to 4K monitors where periodically the monitor will black out for a few seconds.

I never use the upgrade path for new distributions: I always perform a clean new installation, and allow fresh hardware configurations to be generated. This is not an "upgrade" issue.

Observations: I can use a mini-display port connection to the DVI-B input on the monitor (and forego the 4K resolution): In this configuration, the screen black-out issue does not occur. The placement of windows after screens blank is an issue.
I have enabled "Workspaces" because I found that windows would hide on workspaces I could not access without this enabled.

The windows ALWAYS migrate to the workspace to the left of the active one.
This issue only occurs with dual monitors with extended display.

I am now experimenting with disabling monitor power saving (Screens should never black out). I will also experiment with using only the external monitor.

Hardware in use: Dell XPS 15 9530 (the UltraHD touch screen model - it is awesome). Monitor: Kogan Ultra HD 28" display. HDMI cable. Monitor to the right of the laptop display (in case that config matters in the "Displays" configuration.)

I'll report back on the results of "no power off" and "external as only display".

Again - this issue is new to 16.04 for me. 14.04, and 15.10 were rock solid.