Kaby Lake computers with USB Type-C DisplayPort only (non-ThunderBolt) connections using WD15 or DS1000 may have blanking external video If only one monitor is shown, while the other is not, go to the Intel Graphics Control Panel, and under Multiple Displays, select the output for the second monitor.

The alternative is to use just one display at 4K with the HDMI cable. In this setup, we had similar experiences with typing and video watching. Open the Intel HD Graphics Control Panel and go to the Multiple Displays control to set the display to the extended mode. If none of the following articles resolved your issue, there is a new resolution in the following section of this article:I played some 4K video on the display while taking the 10fastfingers.com typing test on the TV, and found that performance didn't stutter at all. The video was smooth, and I managed to type at my average rate of 100 wpm with a 2 percent error rate, and experienced no lag.