Search a few forums and doing a wee test myself, I beive it is the router supplied by vodafone.
Tonight, while watching tv, I did a speed test via speedtest.net. During the download test, the tv stuttered, green lines etc. As soon as the download test finished and the upload began, the issues stopped. Did the test three times- same result everytime.
Searching a few forums, it seems the fix is to replace the router. Some had a new one supplied by vodafone, others bought their own.
I'm interested in what vodafone suggest to you please.