Same issue here on both channels. It's not very often I see something I want to watch on the Ultra HD channel but it's like cutting out for milliseconds at a time. The sound on BT Sports 4K is fine and other things like Firestick and Xbox in 4k are also fine.
Must be a transmission issue surely? Wanted to watch Hans Zimmer but as that is very sound based not much point. Any official word on if it is a fault?