It has worked flawlessly to cast from my android-phone until today when I started to get ads even though I have a subscription. Maybe there's been some update? I haven't used my chromecast with the phone for a week or 2.
If I continue getting ads, I'll cancel my sub since there's no point to it.
I think what may be happening is when the chrome cast is streaming it isn't logging in with the account that has been asked to cast from so it is not logging in so your viewing it as a free guess? it makes sense