Hi @Warcat59,
A warm welcome here in the Roku Community!
We're glad to help you with your problem with streaming Max on your Roku Ultra. Please try to navigate to the channel tile on the Roku home screen, press the * key on your remote, and choose "Remove channel." Next, restart your device from Settings > System > Power > System restart (if you do not see a Power submenu, skip to the next step). After your Roku device restarts, visit the Roku channel store or search and add the channel again. You can also check out this link here for more details on how to resolve a channel playback issue.
Let us know if this works for you!
Best regards,
Eunice
Eunice L.
Roku Community Moderator