Ive been having this issue for approx 8 weeks, Chromecast builtin to my Sony TV and also three chromecasts around the house (same IP), all stop mainly at end of adverts but not before any sky trailers.
I mainly cast from my phone, works direct on phone (ie no casting) but as soon as chromecasting all fail.
I have reset everything, all off (router/switch/phones/tv/chromecasts..... the lot!) then back on, router 1st etc... This does not stop the problem.
The advert signal is throwing the chromecast device, so what can a phone receive and decode ok that a casting device cant?
Needs sorting soon sky chaps, people are not happy, its a bad bug!