sub mini

Maybe it is too close? And Sonos does not support extenders.

Can you post the devices that make up your network and how they are connected? Maybe there is a setting or hardware you need to change.

Wi-Fi usually works best with 3 feet between devices, 2 feet can start to see mutual interference. 

You can't get much help with an extender in the network, just too many possible issues.

Thanks for the responses folks. I have a tplink deco mesh system. All more than 3 feet apart. 

Strange that it worked fine (for over a year) until a few days ago. 

Sudden changes are a way of life when using shared connections like wifi. You can be fine, you do nothing, but a neighbor does and things go odd. Even you doing something that shouldn't impact your wifi can, like my RF noisy NAS that wiped out one of my Sonos speakers. 

I'd say call support for an advanced look at your internal data but they are most likely to balk once they see an extender.

Are you sure you need the extender with your mesh wifi? Maybe replace it with a other mesh node?

Thanks

I've no extender, just a deco mesh network. 

Seems to be working now, with the sub mini wired via Ethernet. 

Finger's crossed!