I just factory reset my Roku after following these steps last week (and them not working) and HBO still won't load. I click on the app, it will show me the HBO opening thing (big blue/purple screen with "HBOMAX" in the center), and then it will show me the black screen with the little floaty white load bubbles at the bottom before returning me to the home screen. My Roku was made in Feb. 2019 and even before the factory reset happened I had reupdated the app and the system. I know it's not my wifi (university wifi is quite good) and I was happily watching HBO the week before last, so I know this is a new problem.
The original issue for this thread has been resolved and we will be closing this thread out.
If you are still experiencing an issue with the HBO Max channel that is related to a black screen and the 3 dots then either an error message pops up or the device returns to the home screen, we would recommend posting in this thread here so we can better assist you: HBO Max Channel Loads and Shows 3 Dots