I'm having the same issues on my X1:
-Never stays in HD quality
-plays fast to catch up or most of the time it errors out.
- Channels always displaying "service is unavailable"
I can't even watch the NFL playoffs because it just sits on th service is unavailable screen.
I get well over 100 mb and I dont experiance any of these issues on Netflix, Hulu, Twitch, VOD etc. This is suppose to be my main source for TV but it's not working out obviously..