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 2, Roku 2 XD, Roku Stick (3600)
Apple TV (4th gen), TiVo, Chromecast
Roku Stick (3500), Roku 1, Roku 2 XS, Roku LT(2400), Roku XDS, Roku XD (2050)
Apple TV (2nd, 3rd gen), FireTV, FireTV Stick