Since we still haven’t received no answer, I’m going to bump this again. I have seen a somewhat similar problem being reported, which apparently can be fixed by downgrading to the 9.28.0.3162 client version. This was not the case for my audio/video desync issue and the problem wasn’t fixed by simply downgrading to the client version.
I’m not sure if the 2 issues are related, since that issue seems to be appearing for 4k content and my audio/video desync issue happens in 1080p content as well.
I will try to tag some of the staff people that seemed to be involved with that topic such as @morganj and @sixones (sorry for the tag).