xfinity stream won't work with chromecast

I'm trying to cast from xfinty stream on my tablet (also tried my phone) and it won't locate the device.  it tells me to make sure the other device is on the same wifi network.  I only have one wifi network and xfinity is the only app that won't connect.  I tried Amazon, hbo max, Peacock, etc. and they all connect instantly.

my tv is new and has built in chromecast.  my xfinity stream app is up to date.

any suggestions?