They do not work reliably if I hook them up to the dock one at a time. Each will work occasionally. But eventually, they start flickering on and off. Sometimes it's constant. Sometimes it's just every few minutes or even every few hours. It just doesn't seem like this dock was ready for prime time yet.
I'll give the active adapter a try with the HDMI monitor. Not sure what to do about the monitor with the DP connection.
I have LG 34UM95-P and Dock at home, and a LG 34UM95C-P and dock at work. Nether can be used on the Dock with DP cables. Screens BLANK out a few times a minute. The C Version will work DP connected directly to the SP4 only Blanking 1 - 2 times an hour. The LG 34UM95-P I needed to use the DP-to-HDMI to make it work without blanking.
IMO the DOCKS are broken. On a different thread I was told there was going to be a firmware update for them, and it differently needed.