Just wanted to leave this here in case your play / pause automations suddenly stopped working: As you may know, the current state of the media entity for Chromecast with Google TV is heavily dependent on the app. Some apps like Netflix seems to not report at all, while others like Apple TV and Youtube have been working reliably.
I noticed a couple of days ago some of my automations relying on this trigger stopped working. I dug a little and found out that just Youtube stopped reporting play state properly.
This seems not to be a HA issue. I made a Google Home routine with the same trigger, and is behaving in a similar way. Looks like a fix is needed on the Youtube app itself