So, even though the V6 box has its own dedicated line through the co-ax cable, you are saying that the Netflix app uses either LAN or WiFi feed. Is that correct?
The powerline unit upstairs is plugged directly into a mains socket. Downstairs, it is plugged into a multipoint. Could this be the cause of the instability? I have ordered new powerline units with passthrough power sockets so that I do not have to use a multipoint downstairs.