On 2 different roku TVs, and 2 different models of the stick, I have attempted private listening with the app on my android phone.
While it may be possible that the problem is my phone, I don't have any other "slowness" problems with the phone. I also understand that A/V synchronization is not an easy thing to manage, and there are many variables here for the folks at ROKU to deal with:
Speed/model of phone, model of remote, If bluetooth is in use on phone, speed of network, etc. (and of course the human brain).
For me, no matter what I do, the audio is at a delay that is unnerving and I find it "unacceptable" for use.
The FAQ on this says "If audio is out of sync: Software will make attempts to auto-correct itself. Wait a moment before troubleshooting."
It never auto-corrects to something that I find reasonable to experience.
A/V synch is fine when using TV/HDMI.
Is there a way for me, the user, to force a higher video delay when using private listening (hidden menu, advanced menus)? Is there a way for me to force private-listening to try to re-synch?
Mine (on an iphone) mostly starts out in pretty close sync but can can drift out with wifi glitches that only seem to happen when streaming video to the TV over wifi while also using the app with private listening. In this case disconnecting the private listening and reconnecting have fixed it for me, but I've seen posts here where others suggest disconnecting power to the TV and restarting to get audio completely back in sync.