iMac 5K issue with ext. 4K screen

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Just few days ago I switched from triple display setup (5K + 2 x FullHD) to double setup (5K + 4K) for my late 2014 iMac 5K. The new display is Philips BDM4350UC connected via mini display port to display port cable. It runs in 4K @ 60 Hz (had to switch display port 1.1 to 1.2 in display menu). Image quality is great, however I have very annoying problem with waking up iMac from sleep:

1. Sometimes everything is ok and both screens wake
2. Sometimes only external screen wakes and reboot is only way to wake iMac screen
3. Sometimes both screens remain in sleep mode (system works, but both screens are dark) - in this situation I have to switch computer off with the button

I've searched the web and found posts about similar problem, however no solution. Have anybody had similar issue and maybe know solution?

Is there software way to wake up displays (tried resetting finder with no luck)?

 

[ahostmadsen]

Did you upgrade to 10.12.4? It solved wake issues with my 4K screen and MacBook. Might be a different issue, but if you didn't upgrade, worth a try.