Goolge WiFi, the network provider and the decoder.
I have a Google WiFi setup I bought a few years ago. At the time I just plugged it into the box provided to me by the ISP and thought not much more about it. It just worked. As it turns out the network governed by the ISP router could not route to the Google WiFi Mesh. The other direction - from a device in the mesh to a device in the rest of the network routed just fine. I decided to let the Google WiFi Mesh be the only network. I configured the ISP router to be in brige mode, configured the Google WiFi Gateway to use the address range used by the ISP router (192.168.10.x it was originally set to be 192.168.86.x). I even purchased a switch with 8 ports - to be able to plug in everything (Philips Hue, Telldus, Raspbery, Onkyo Receiver, the TV and last but not least the decoder).