In my case, it "works" but only audio plays. It's like the screensaver doesn't notice that it has to stop rendering, until I press a button in the controller and it gets fixed.
Uninstalling the Builtin Chromecast app and reinstalling it again fixed the problem until it started happening again.
All in all I wonder google are adding these bugs intentionally so that people still have to buy chromecasts.
Honestly the whole casting feature is pretty shit and unreliable. My Bravia never had any issue with casting, meanwhile my "godly" Shield works like 50% of the time. There shouldnt be that much of a variety between implementations, unless the whole platform is shit.
Try to uninstall the Chromecast update and turn off auto app updates.
One update breaks it and the next one fixes it, that's Google in a nutshell.
I know that when I have this issue with my Sony Bravia TVs, the first thing I do is open the Play Store and search for "Chromecast Built-in", "Chromecast Receiver" or "Google Cast Receiver" and see if there are updates. For some reason, that app on my TV doesn't auto-update itself.
I find the most reliable way for me to fix it (which still only works half the time) is to tell my Google home to open Netflix/YouTube and once it talks to the Google home, it's wakes it up for my phone to be able to cast.
I find a full power cycle tends to fix it on mine...