This doesn't fix the problem. I believe spotify has pulled support for Vizio chromecast TV's. I have the same exact problem and nothing I've done has fixed it. I've restarted the TV, router, reinstalled apps and still nothing. Such a shame.
Noticed the issue with my iPhone X on two different SmartCast TVs from Vizio. I did a factory reset to the tv yesterday and it got it working for a few hours. No back to nothing... every other app casts fine. Seems like an issue with the current build of the app?
They must be pulling support for Cast... They remove features, refuse to fix issues, refuse to publish release notes (very unprofessional in the developer community, and a very shady practice), and continue to raise prices.