Thanks, @Robert_Fielder!
Are you able to temporarily connect the Core machine to the network via the same WiFi connection as the remotes? If so, is there any change?
As mentioned below by AJ, you cannot use Google WiFi as a bridge in a mesh configuration:
https://support.google.com/wifi/answer/6240987?hl=en
If you’re creating a mesh network with multiple Wifi points, your Primary Wifi point cannot be in Bridge mode. This is because the Primary Wifi point needs to do special things to control settings and communication within your Wi-Fi network. If it’s in bridge mode, you’ll lose some of Google Wifi’s key features.
Thanks,
Dylan