The pciture of TUDN channel is cropped in Xfinity Beta on LG Oled TV but it is fine in https://xfinity.com/stream ; you can see it in the score in the next pictures.
I moved your post to the stream app area of the forum. That sounds like your TV's setting is set to zoom. is that an SD or HD channel? Can you describe cropped? note that the images in your post are hidden until approved by a Comcast admin.
It is not the zoom setting since the other channels are not affected (I just checked again, for instance espn is ok); also, sometimes when the same match was on more than one channel I switched between channels and only TUDN had the picture cropped even though the origin of the transmition was the same channel; (what I mean with cropped is like you said it looks like as if the image is zoomed in to the center). First, I though I was something with the rigths and that the picture was intentional cropped to cover some brands or similar but then I noticed in the website is ok.
I only tried with HD channels before but I just tried with SD, it is also cropped and in this case it is in format 4:3.