Hi, I have a similar problem with audio lagging several seconds behind video.
Player: model 3700X Roku Express. Software 9.20 build 4131-28
The problem occurs only on Amazon Prime. I had not watched Amazon for a year, but started watching when new season of Man in the High Castle dropped. You had a firmware update just before I started watching again. Last year I did not have this problem. The problem does not occur in Hulu or Netflix, or on any other HDMI sources. The player goes thru an audio extractor before going to the TV. The extracted analog audio goes to a vintage Dolby Pro Logic AV receiver. The TV audio is muted and not used. I would like the option of rolling back my firmware as nothing I have tried in the settings works.
I have the Roku Express, which does not have those audio options. It just has Stereo, dolby, DTS, etc. No "off". The only audio menu with an "off" option is the menu volume, where it sets the volume of the clicks and chimes when you make a selection. But that has nothing to do with playing content.
What model Roku do you have? I might consider that one if you have found a solution for it.
I previously posted about having this problem with an older Roku Express connected through HDMI to a 5 year old Elements TV. Until the past month performance was flawless but now I have this out of sync audio issue. When I first select an app from ROKU the audio is in sync and then slowly it gets increasingly out of sync the longer I am connected. If I exit the app and then go straight back in the sound is sync'd again but over time the problem repeats. I have FIOS so no network lags and other HDMI inputs to the TV have no issues. I do not have a sound bar or any additional sound devices connected to the TV so its hard to imagine the problem could be caused by anything other than the Roku. This seems to be a problem that only started recently and there are reports this impacts many different channels so instead of ignoring this issue I am hoping Roku will provide a solution.