you may have already alluded to trying this, but when i ran into this problem as well (or similar), I put the DK2 in the first video port (happens to be DVI), and then when UE4 didn’t recognize the DK2, i ran the demo scene. demo scene ran fine, so closed out, and then opened UE4 after which it worked. this was in extended mode. not really sure of the logic here, but that sequence worked on different two machines.
yeah, rolling back the drivers did nothing but make me even more frustrated than I already was. I wasted 3 nights in a row staying up late after work trying out all the suggested fixes I found online.
All I got was bluescreens, and Unreal crashing every time I retried to open my Project done in 4.8
I’m just going to go back and recreate my project with 4.7