I don't know if the hardware on the voda tv boxes has been updated in recent years, but in the early years (remember it's been around since 2010) there were issues being seen with HDMI and Samsung tv's (search the ancient forums on geekzone). Flicking to using component cable solved the problem but broke the deal on reasonable expectations of compatibility.

HDMI has been through a lot of revisions, and chip vendors are notorious for the 'good enough' approach to market. I suspect you have an unhappy combo that no amount of set top box replacements will repair.

Happy to be proved wrong though!