There is nothing that im aware. Casting to this device from anywhere else on the network works ok. I figured core might be blocking the google device do to security / cert / firewall rules that may be in place.
I can leave this function elsewhere in the system i just thought i would see if anyone else had run into issues.
Now… I’m running HA both on a different platform but it’s also the supervised version. Still before any TTS would work for me, I needed to add an URL in the settings/system/network. Perhaps this can be something for you to check and/or try?