Flickering 4k@60Hz monitor

I have bought new laptop Dell xps 15 9500, installed Ubuntu and tried to connect external monitor, but got some problems. If I choose 4k@60Hz monitor occasionally got blank which make it unuseable. I don't have this problem when I use awindows (dual boot), so I suppose there is a problem with Ubuntu. Also I don't have this problem, when I choose 1920@60Hz, but problem occurs with 4k@30Hz.

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