Hi @Malcolm_Bradley,
Welcome to the forum!
Can you please use this thread as a guide and provide additional info regarding your setup?
It would be difficult to help without understanding the basic info of how you have your system set up, basic details such as:
- Core model/manufacturer
- Networking gear in use
- If this issue only impacts the Sonos speakers (for example, does “System Output” on the Core work as expected)?
- How the Core and Sonos fit into the network setup - are they both connected directly to the router via Ethernet?