We have 7x SP3 (3 I7 and 4 I5). We have 8 SP3 Docks whereof 3 have been bought in United States and 5 have been delivered from Germany. All SP3's updated fully with all updates (and yes, no fan noice).
Have both Samsung 4K monitor and multiple other. Dock flickers and shows a picture for 0.5 seconds and blinks regularly (every 15-20 seconds or so turns on and then off again immediately after 0.5 second). In 100% of all cases not been able to show a picture
from any dock or any device when using mini-displayport to displayport consistently. We have tried with both adapters and mini displayport to displayport cables.
Result no matter type of 4K monitor is as written by others that you with a mini displayport to displayport, directly in the SP3 (no dock) in 100% of cases will always get a maximum resolution of 2560x1600.
You can directly through the SP3's own mini displayport with any 4K monitor get a 4K picture in 30Hz (not 60Hz as supported by displayport 1.2), if you attach a mini displayport to HDMI adapter to HDMI on monitor.
We can in 100% of cases get a 1920x1080 picture with any monitor, connecting a mini displayport to VGA cable to the dock.
We have tried everything from combining different docks with different SP3's, different cables, different brands of monitors and drivers from manufacturers. Situation and conclusion as it stands now is that 100% of all SP3 Docking stations delivered from
both united States and Germany does not support mini displayport to displayport connections.
Hoping and praying its a software issue.