UE 4.27 VR Template Black screen

So I wanted to try the new VR template in 4.27 using OpenXR after watching the stream.
Currently I am trying to run it with the HP Reverb G2, in the stream they noted that it has been tested with this HMD and that it should work. You only need to enable the HP Reverb G2 Motion Controllers plugin for seeing the right controllers.

However, when trying to play the VR preview I only get a black screen.
I did a fresh UE 4.27 install and created a new project using the VR template without changing anything.
On this machine I also use a Vive headset so I made sure to close all programs associated with that HMD and even disabled SteamVR so OpenXR would find the correct runtime.
And yes, Windows Mixed Reality portal is running so it should find this.
Restarted the editor, the machine, reconnected the headset but nothing seems to work.

Has anybody had a similar issue or does anyone know what it might be? (also had this issue with 4.26 but hoped OpenXR would be better)

Check to make sure that either Windows Mixed Reality or SteamVR is set to be the OpenXR Runtime. You can change that in SteamVR or use this handy tool: Introduction to OpenXR Explorer - Microsoft Tech Community

So I did a fresh Windows install with UE 4.27 and opened the Template. It did not work by default even though WMR was the only OpenXR Runtime (SteamVR isn’t installed). Using the tool you described and manually setting it did the trick.
Converting an existing 4.26 project to UE 4.27 the HMD did work but I couldn’t get the controllers to work. Migrating everything to the VR template and re-adding the controls did the trick and now it seems to be working.

I will test this method on another system soon where also SteamVR headsets are installed.