The problem exists on the Virgin TV Go application (that uses Chrome) for BT Sport 3 HD - the problem has existed for months now and you will find other threads reporting the same issue. I think this is amazing that it's not been fixed yet. What information do you need to resolve the issue? Can you share your test setup that it is working correctly with?
My Chrome version:
BT Sport 3 is shown in the correct widescreen aspect ratio on the channel list:
however, when selecting the channel the content is in 4:3 and squeezed tall in windowed mode and full screen. On full screen there are 2 black bars wither side.
..edit to add.. the problem appears to be resolved now.. thanks.
(either that or I've corrected it myself with an extension I've been playing with!)