Hi have the same issue!
If I open the steamVR mirror I can see at the right edge a small part of the unreal scene.
But the rest looks like there is a black plane in front of the camera.
very weird.
I think it has to do something with the new steamVR drivers, multimonitor, windowed / fullscreen mode of unreal.
I tried to start the project in -windowed mode via command line flag on the build exe file. I can then see the scene normally but the vive hmd is not starting up.
can you please reopen this ticket?