Hickups on the external monitor connected to closed laptop

 * Cinnamon 3.6.7
 * Mint 18.3
 * Kernel 4.10.0-42, Intel HD Graphics 530 (Skylake GT2), kernel module i915, Xorg intel module
 * 64 bit

Issue
Found on Dell Latitude E5470 laptop, with external Dell U2515H 2540x1440 monitor connected by HDMI cable. When the laptop is open, everything looks good: I drag apps between the laptop's 1080p screen and the external 1440p, display playing video on the one screen or another, and see no lags at all. When I close lid, the laptop pushes image to the external monitor (dconf's lid-close-suspend-with-external-monitor value is set to false to keep laptop awake), and any move starts to hiccup, a little, it repeats every ~20-30 seconds, each hangs for a ~second.

Steps to reproduce

• Connect Dell Latitude E5470 to external HDMI monitor
• Make sure that 'dconf read /org/cinnamon/settings-daemon/plugins/power/lid-close-suspend-with-external-monitor' command returns false or nothing, otherwise reset it
• Close the lid
• Just make image moving (e.g. play any video file)

Other information
Also tested on the same hardware and Mint 18.3 + KDE, and found no issues.

Start by reproducing the periodic hangs with the dconf setting /org/cinnamon/settings-daemon/plugins/power/lid-close-suspend-with-external-monitor set to false, using the listed Dell hardware and HDMI monitor. Compare behavior with the lid open and with KDE, and use the Cinnamon power-management path as the entry point. Done means the external display remains smooth while the closed laptop stays awake.