Fyi at some point I could no longer ask my Alexa Dot to “Play Some Music” with it then playing on my preferred Sonos speaker. To be clear I am not referring to commanding the built-in Alexa on the Sonos speaker itself. I am commanding the Alexa Dot with my music choice which is then being re-routed to the preferred Sonos speaker (as to avoid listening to music on the small anemic speaker inside the Alexa Dot).
First step in troubleshooting this issue: I confirmed all Sonos speakers were working as they should via the Sonos app.
In the Sonos app I also confirmed that the particular Sonos speaker I wanted to integrate with my Alexa Dot was indeed logged into the same Alexa/Amazon Voice Assistant Account as the associated Alexa Dot (not sure if this is necessary or not).
I then went through the current list of Devices in the Alexa app and deleted/trashed all existing Sonos speakers.
I then disabled the Sonos skill in the Alexa app.
I then re-enabled the Sonos skill in the Alexa app. This in turn led to a screen where it detected available Sonos speakers, of which all my Sonos speakers appeared. I hit “Done”.
In the Alexa app I then went to the existing Group I had already created which already included the associated Alexa Dot and set the Preferred Speaker to the particular Sonos speaker I wanted to here the Dot-prompted music through. Viola working again!
I seem to need to go through this “Alexa Dot Sonos Speaker Reestablishment Routine” a few times a year.