My older Roku Express is doing the same thing. I have used two different iPhones, a 6 and an 8, both plug in and wireless (Bluetooth) headsets (4 different Bluetooth), and nothing has helped. It just started a bit over a year ago, and I have had the AOC TV and the Roku since prior to 2017, and never had the problem before. I have tried all of the suggestions you guys have given that pertain to the Roku Express and didn't involve uninstalling things.
There is no apparent problem with ANY of the channels on the Roku working properly on my TV, but not properly on my Bluetooth devices.
It would be nice to have an actual fix for this, or if it is not possible, to actually know what is wrong. I can listen on my iPhone without losing sound, and I can listen to my iPhone on other apps without losing sound, so it seems as though it must be the ROKU app or the way it is interfacing with the iPhone. Please be so kind as to give my the fix.
It appears you are only experiencing an issue with the Roku mobile app private listening feature and not through the TV sound. Can you please clarify the issue you are experiencing? What specific Roku model device are you using? Have you already tried changing the wireless channel on your wireless router to minimize wireless interference?
With more detailed information, we will be able to assist you further.