Maybe, but it's on HBO's end if that's the root of the problem. Everything else works fine and, in this greediest of ages, we can be sure that HBO isn't the only provider implementing DRM.
It's been half a lifetime now, but I've done some Apple TV and iOS development. There's a concept of the audio path and your app absolutely receives information from the OS about the state of the audio path and any changes to it. For example, your app will receive a message from iOS telling it that the headphones have been unplugged (if wired) or otherwise disconnected (bluetooth).
For 20 years, Apple's instructions to developers has been something akin to "if a new audio path was just added, switch audio to it if already playing ... if the path you were playing on got removed, pause playing" (obvious, huh?). Everyone gets this right except, unless they've fixed it in the last couple weeks, Audible. The dozens of times I've pulled my AirPods out of my ears only to have some embarrassingly low-quality audio book start blasting from the phone speaker at maximum volume has been infuriating.
The point is, it's an Apple platform, but 3rd parties must show pride in their work. It's easy to imagine HBO shipping the update that broke playback for all of us simply because their lowest-bidder software development partner coded the app to deal with only audio source zero (or some similar default) because that worked on their single test Apple TV, which itself was connected directly to a $150 Black Friday TV. They may have used sample code from the internet that has a placeholder to the effect of "Place your app's audio path handling code here".
Such is the effect of outsourcing everything, but dang, it'd sure be nice if Apple had mandated that their player own playing and (DRM) protecting the content, even if that meant the video itself was just a frame in the 3rd-party app. Maybe we'd still have to log-in whenever least convenient, new shows wouldn't show up in the episode list without an app restart, etc... But the video and audio, once we got it playing, would just freaking work!
