I have the same problem but with Netplus (Fribourg). I contacted TP-Link support and they are aware of this problem (caused by IGMP). Apparently there is a beta firmware, which I have requested by email. I am still waiting for an answer, I will post information here as soon as I have something new.
I have the impression that there is real chaos in the area of compatibility between Powerline models and IPTV from the various providers. No one seems to know what exactly works together or not.

First, take a look at this guide from Sunrise:
https://www.sunrise.ch/content...
Have you connected everything (modem, router, box) as shown there? It's Devolo there, but the principle is the same.