Macbook randomly shutdown 4k external monitor

I would put a lot of weight in a technician that sees many macs as they really don't have any reason to mislead you. You can also get a second opinion if you don't feel the one you got the first quote listened to your concerns or explained how he arrived at that guess.

Do make sure you look carefully - when the backlight goes out on a LCD - there is so little light coming through it is hard to tell if the panel is drawing fine and the light is missing or the panel isn't being driven.

Without opening the mac and trying to replace things (and especially when it's intermittent) it's hard to know for sure what one piece is failing. If you ask a tech to put percentage chance you will find most situations have multiple causes, but one is much more likely given experience and symptoms.

The next time it goes out - you can use a flashlight to narrow down if the panel itself is not getting signal or it's just the backlight by looking for the menu and other graphics on the screen getting drawn.

Troubleshooting steps

• Try different cable

• Check Console log to find out the reason

• Disable Graphics switching

• Open ColorSync utility (in Utility folder) to see if the display is there and what driver is selected.

UPDATE:

From your Console log

Found 111 modes for display 0x003f003d [111, 0]

System is having problem to select which mode to use.

Open ColorSync utility and set the current profile to same profile as Factory.