My Sonos One has recently started saying “sorry this device is offline”.
I have disabled and re enabled via upgraded Sonos app. Updated software on Sonos one.
Deregisterd and re registered via Alexa App.
Both apps report device is online via wifi.
Maybe try de-registering each of the Sonos components in the Alexa App, as there is both a ‘speaker’ component and an ‘Alexa’ component for each Sonos speaker (and fyi a TV component for a Sonos HT product). The Alexa component is often (but not always) embedded inside the speaker component in the Alexa App device list. When they are all removed - remove the voice assistant from your Sonos speaker and reboot it. Whilst it’s rebooting, remove the ‘Sonos Skill’ from the Alexa App.
Let your speaker(s) reconnect online and settle, post reboot …and then simply reinstall the Alexa voice assistant to the speaker via the Sonos App. This will auto-reinstall the ‘Sonos Skill’ in the Alexa App and then see if that fixes your issue. If not try removing/reauthorising your default music service in both the Sonos App and the Alexa App.
If problems persist after that, then It maybe best to submit a system diagnostic and either note/post it’s reference back here and then contact/chat with Sonos Support Staff via this LINK and see what the Staff can suggest to resolve the issue.
Thank you so much. I’ll give this a go. 
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