I've got this happening as well.
I've got two Surface Pro 3's - both Windows updated with everything.
We have two docks as well. Both docks using a generic MiniDP to HDMI cable. Some are from CableMatters - others generic in that I can't tell if they came with a brand name - I've got a drawer full and have tried a bunch.
One Dock is attached to a ViewSonic VX2753. The other to a ViewSonic VX2770.
Surface A on Dock A with Monitor A (2770) Works as you'd expect.
Surface B on Dock B with Monitor B (2753) - does not recognize the monitor.
If I put Surface A in Dock B, it works (with Monitor B).
If I put Surface B in Dock A, it works (with Monitor A).
Circumventing the Dock always works with all monitor/surface combos.
I just cannot get Surface B to work in Dock B with attached to Monitor B.
Early on in trying to troubleshoot this, I did try using a different monitor (exactly the same as monitor B - VX2753 -) and it didn't work. BUT... I uninstalled the Intel graphics driver completely, rebooted, ran windows update, installed the graphics
driver again, rebooted (shutdown/turn on) and then restarted (just windows-x, restart) and it STARTED WORKING!. Then, I had to rearrange the desk to set up the working monitor - required unplugging things etc., so had shut down the surface and the monitor.
ONce things were arranged again, I was back to the original state of non-working external monitor (with the same hardware that was working when I shut everything off).
If all of this hasn't confused you, thank you for keeping up - I'm going to see if there's any movement on this thread over the next few days. If nothing helpful comes up, I may be packing up a truck and heading to the MS store to see if I can get some
help there...
I do realize that it seems like just having the two folks in question trade docks would get them both working, but if there's something wrong, I'd prefer to at least identify it before taking a risk with it happening again further down the road. And if
it's something that requires a hardware return/exchange, I would prefer to do that, rather than just hide the problem and cross my fingers.
Any help/suggestions would be appreciated. Thanks!