The issue doesn't happen locally playing from the Quest folders. It happens connecting to XBVR's web interface where playing anything only shows a black square and plays audio. In fact, if I play a local video it plays behind the Heresphere menu and if I try to play a video from XBVR the original local video remains behind the user menu.
Are you enabling the HereSphere web API when using XBVR? You need to press the icon that looks like a play button overlaid on 4 tiles to the left of the url input box. That'll load the web API, which will allow you to stream the videos in VR. If you only use the XBVR UI in the web browser, then the videos probably won't play properly, because it's relying on the embedded web browser to play the video.
I figured it out. There is a toggle by the URL search bar to turn on streaming apis. I didn't see it documented but seems to be an important thing to note!
