Thanks for the response, it’s 4K77 UHD v1.0. I also have the 1080p Grindhouse version, but was kinda hoping to make use of the 4K monitor I bought the other day.
Looking at the bitrates, it seems 4K77 is considerably higher than 4K83, so I wonder if the Panasonic player can’t handle bitrates that high over USB (although the USB stick is USB 3).
I also have an XBone S, I’ll try playing it on that later this week, although some posts on Reddit seem to indicate that the audio has to be Dolby Digital.