Bumped into this thread while browsing the VR sub-forum. I sometimes have the brief blackout in the Reverb G2 also.
One guaranteed way to trigger it is to open the Sky4Sim window in VR. When it initialises, it creates a sudden drop in frame rates and almost always causes the headset to blackout for a few seconds. If I close the window and re-open it, it re-initialises and does it again. It can also do it when I drag or zoom the map around in the Sky4Sim window.
So I suspect it’s heavy CPU load that triggers it most often.
A few times, I’ve had it black out completely (and stay black) just a few seconds after starting up VR. Restarting WMR and other elements doesn’t fully fix it, even unplugging (power + USB both) and restarting the headset. The image might come back only briefly, but audio remains. This can happen in other games, in WMR and SteamVR, and usually if I’ve run multiple games back-to-back or loaded MSFS more than once. The only full fix for that is to restart the PC, then everything is fine again.