I have a MacBook Pro Retina 15" Mid 2015 running Mac OS X 10.11 (El Capitan) and I have a Samsung U32D970Q 4K external display that I would like to use in a closed clamshell mode through displayport to get 4K at 60Hz.
When I try to wake up MacBook my external display is not waking up. This happens randomly. In such case I have to disconnect the cable from the display port connection, open up the MacBook and reconnect it again. Sometimes only restarting MacBook solves the problem.
Previously I used my older MacBook in this setup but instead of a display port connector I used HDMI (but with only 30Hz, that is why I want to connect with displayport) and everything worked great.
Now, when I am connecting through displayport with new MacBook, I can’t find reason why is this happening. Is there any issue with displayport on new MacBook or Mac OS X?