This was very similar with the Z9S. I suspect there is something to do with Android and 3D playback. Not just with ISO files but non ISO 3D rips, while playback is fine, there is extremely limited response to any remote control command, like pause, stop, chapters, forward, etc... It is like the remote was dead.
I was hoping the Z9X would be an improved experience, since it is Android 9 vs 7 on the Z9S but nope. I just tested it yesterday. If you are OK watching the entire movie without any adjustment of the audio stream or subtitles and willing not to take a restroom break then it is fine. But there is no way to stop the movie... And you have to watch it until the last frame to gain back the control of your media player. Alternative is the ON/OFF switch.
BTW I had the same experience with the Himedia Q10Pro device.
I hope a future firmware will address this.