We get green lines/ freezing/ pixelation often- especially when there are a few family members at home, connected to the internet- fibre with two vodafone tv boxes.
Tonight, with not many connections, I did a speedtest and noticed lots of green lines and freezing while at the download test (96Mbps). As soon as the upload test begun, the issue stopped. Did the test three times- same result each time.
Searching various forums, I see others have had the issue and resolved it with new router- some supplied by vodafone, some supplied thier own.
If you're still having this issue can you please confirm if your Vodafone decoders are connected directly to the Vodafone supplied router and if you have any addional networking equipment connected such as other wireless routers or access points, switches, hubs etc. Did the lines appear on both deocders when you did the speed test?