Not sure if any other V6 users have this problem... we have constant issues with lip sync issues on Amazon Prime on both V6 boxes we have at home. Problem has been there since we got Virgin in November last year. The video is noticeably (say 1 second!) behind the audio.
Normal channels, Netflix and iPlayer all fine by the way.
I have issues with Prime even on my desktop with it being out of sync. Seems like it's just an Amazon issue, you could try connect the V6 up via Hardwired and see if that works. Also Manually setting resolution from "auto" to whichever your TV resolution is. See if that works.
** I work for Virgin Media - but all opinions posted here are my own
The main V6 box is hardwired (not WiFi). Tried changing the output to 1080p instead of auto, doesn’t seem to have changed anything, The thing that bothers me is that it’s very consistently behind on all video, including the live football on Prime, which makes me suspect it’s a local issue not an Amazon one