Thanks for reaching out to the Roku community!
I'd be happy to take a closer look to see how we can help get you up and running.
We recommend starting here to troubleshoot channel issues: Follow these steps in order:
1. Navigate to the channel tile on the Roku home screen, press the * key on your remote, and choose 'Remove channel'.
2. Next, restart your device from Settings>System>System restart. (For Roku TV Settings>System>Power>System restart)
3. Once your player/TV starts up again, go to 'Streaming Channels' on the Home screen, and add the channel back once more.
In addition, make sure that you get the latest HBO Max channel version by checking for a channel update using your * button on the channel tile, or going to Settings for a System Update there. Then, restart your player.
You may also refer to this link: How do I resolve channel playback issues?
Let us know how it goes! We're hoping this will work for you.