Cannot cast to tv via Xfinity Stream

I recently bought a new sony TV.  When I try to cast Xfinity stream, it tells me to make sure the device I'm trying to cast to is on the same network as my phone (or tablet when I tried that).  I only have one network, so they're all on the same one.  I had no issues with my older tv.  I tested netflix, hbo max, youtube, peacock and disney, and they all located my tv and connected.  It's just Xfinity, which makes no sense given it's an xfinity app, xfinity gateway and xfinity internet service.

Any solutions?

I tried everything I can think of--restarting the TV, restarting the gateway, restarting my phone, clearing cache's, making sure everything is up to date, etc.  

I'm trying to cast a show I recorded on TV.  DRV recordings often suck as they freeze and skip, but the playback via xfinity stream usually works fine--so I often cast my recordings from my phone or tablet to my tv rather than watching the recording on the tv.