While I don't have HBO, one of the kids has service, and the channel on her Roku. It played an episode of True Blood without issue this morning. So, either the issue has cleared up, or it's localized to your area (or your Roku).
Perhaps removing the channel and reinstalling might help.
Roku 3, Roku HDMI Streaming Stick
Apple TV, TiVo, FireTV Stick, Chromecast
Roku LT, Roku 1, Roku 2 XS, Roku 2 XD, Roku 2 HD, Roku XD|S, Roku XD, Roku HD