Why can't you see the screen on Roku when you fast forward? You have to keep guessing when to stop. it's a really horrible experience. I switched back from YouTube tv but we are rethinking that right now.
I moved your post to the stream app area of the forum. Currently the Xfinity stream app does not build/send to the display the thumbnail images you see on some apps. have you tried the voice remote feature of the roku? If you don't have a voice remote roku remote, you can link a smart phone/tablet to the roku device and use the device for a smart remote.