Hello, I have problem with display flickering, blicking and turning off especially when mobile signal is low or while I am calling. This problem remains from the beginning. I tought that android update solve this issue but unfortunatelly, update did not solve it. Is there any possibility how to solve above mentioned problem? Thank you for advices.

update to the latest Firmware 20170622 and perform a factory reset in recovery after that.

wipe data/factory reset in recovery (this will delete your data/settings):
- Power off and then press Power and Volume-up together for around 10 Seconds
- be sure that the little arrow point on recovery (select with volume up, enter with volume down)
- Then the open android with red triangle+"no command" is shown - press Power and Volume up together again
- Select Wipe data/factory reset with volume keys, confirm with power
- After factory reset select reboot system now

Please report if this solved your issue or not.