The key here is that it is ONLY the 1080 channels. The ones streaming in 720 are fine.
I tried it on my Classic (wired connection) (CA: Sportsnet EAST, CA: Sportsnet EAST B, CA: Sportsnet Pacific) and they all microfreeze (video only).
Sportnet Ontario is 720 feed and has no such issues.
I tried switching to Backup player, TS streaming format, etc.. And some combinations are worse than others.
I would have liked to try directly on the NHL channels, but even though both the NHL Arizona and Boston channels EPG shows the game, the stream is not there.