How to run VR Preview from command line 4.12

We’ve been testing our game running an the uncooked version from command line to start up VR preview.
We’ve been using “C:…\MyProj.uproject” /Game/Levels/PlayerClassTestMap?listen -game -fullscreen -log -nosteam.
In 4.11 the -fullscreen flag would bring up (and still does) the game in VR Preview enabling the headset and controllers.
However, now that we’ve upgraded our project to 4.12(.5) this no longer works and the VR headset no longer displays the game world.
VR Preview does work correctly when running it from inside the editor Play > VR Preview (in both 4.11 & 4.12).

Help would be much appreciated.

My project (for HTC Vive) works well in VR when I launch its executable with “-vr” option.