Hi @GrantWilson, thank you for reaching out, and welcome to the Sonos community. I appreciate your detailed post describing the issue. Let me help you with this.
I'd like to suggest the following steps to see if this would work for you.
1. Disconnect WiFi extenders from the power to ensure that your Sonos will connect to your main router.
2. Wire one of your speakers to your router via ethernet cable. SonosNet is recommended to broadcast the same wireless signal to your other speakers.
Please submit a diagnostic to check further on your concern and find out what’s going on. Also, it would be great if you can provide us your network setup including the make and model for each device.
If you need help with any other information, feel free to reach out. We'll wait for your reply.
Number 2 is the most important. Sonos doesn’t play well with other mesh networks, due to the way those networks operate, in conflict with the need for Sonos to intercommunicate with each device.