It could be several things. I’d probably try a factory reset of just that one speaker, so you don’t lose any information that is stored on your other speakers. 

I’d also look at the potential for wifi interference . It could be that while that speaker is getting a good signal from another speaker, it is having trouble communicating with your router on its own, and consequently the outside world. 

It’s good that you’ve confirmed that everything is up to date. But if neither of the solutions above end up panning out, I’d recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Thank you Bruce,

I'll try these differents options. 

I'll get back to you if needed.

Phil