What set top box are you using? I can't vouch for it, but according to one user in this thread switching to one of the newer Spectrum boxes resolved their issue. Others in the thread said it made no difference.
The cable company doesn't have the bandwidth to show all games in HD, especially when there are 8 or so going on at once. NHL CI is competing with the NBA package, multi-channel premiums, and all the other content bening sent down the pipe in HD.
I wish you asked here first, becuase I would have recommended you purchase NHL.tv , as it is guaranteed to have every game in HD provided you have the bandwidth. It's the same price, and you can "take it wth you" on your phone and laptop. You can watch at home via Roku.
I used NHL.tv to watch the Rangers when I was shipped to Wisconsin for 3 seasons.