Have you upgraded the oculus runtime, drivers etc to 1.3.0 on your pc? That version does still work with the DK2 hardware, its not just for the consumer version. Oh yes and graphics card drivers may need an update too in order to get the best of oculus 1.3.0 stuff.
Game engines have generally been updating VR compatibility-related libraries etc very quickly because the vast bulk of their users require it for their users. I know its no fun tripping over the bleeding edge when your particular case doesn’t demand you be there, but its what the bulk of people need so you are probably going to get dragged along for the ride or have to stick with versions of UE4 other than the very latest.
Apologies in advance if I’m barking up the wrong tree, and please note I haven’t actually tried UE4 with 1.3.0 myself. But I do have a DK2 working with Oculus 1.3.0 stuff.