We're having issues using Google Chrome/TV with Now TV (both using as an app on Google TV and when trying to cast from our phones). It will play adverts but not play any of the show itself. The shows play fine on our phones, just not when casted.
Have tried signing in & out of the app on my phone and have only just signed into it on Google TV. Anything else to try?
I have a Chromecast Google 4K TV with the supplied remote and the NOW App runs fine for me.
I don't tend to use it anymore, but that's another story.
I don't use the Chromecast feature on Google TV so can't really confirm if it's working or not when watching NOW content.
I do have Boost and don't get the commercial adverts (just NOW trailers) so I don't know if this is having any bearing (it shouldn't but I have seen a few different reports of glitches / bugs when not using Boost).
Do you have Mobile data on your smartphone, if so perhaps try temporary using your smartphone has a wifi hotspot (if it's possible on the Google TV) and delete the NOW App and download a fresh version from the Chromecast Google TV Apps Store and see if anything plays.
If the adverts wouldn't also play I would have said that it might have been a VPN or regional setting causing the problem.
Apart from the above the only other things I could suggest is unplugging the power to the Router and Google TV for a minute or two, clear cache or last resort undertake a factory reset on the Google TV.