We apologize this has been your experience.
If the issue is only with the channel alone, this is a good indication that there is likely an issue within that specific channel that will need to be addressed with an update from the channel publisher. Channels on Roku are created and maintained by each channel publisher. In this case, you'll want to reach out to HBO Max support directly to share your feedback.
You can them here: HBO Max Support
Tried that. Spent an hour with them. It's a shame because I love my Roku but this is the second time this has happened. I have an Ultra now and the same thing happened on my previous Roku. Once it happens, good luck ever getting HBO Max to work on your box. I have an Amazon Firebox, and an Apple TV. None of those other boxes have had this happen. Right now, this issue is a deal killer for me because I watch HBOMax all the time. If the Roku cannot consistently work with the HBOMax software then it is of no use to me. HBO says it's on your end, you say it's on their end....as an end user I couldn't care less whose fault it is. The other devices work and as an end user that is really all that matters to me. You guys need to fix this.