Hi carj...,
The B2 music from the last session maybe stored in the Sonos's queueing system and needs to be cleared using the Sonos app. This will probably be the case if Sonos was left powered on.
I would power the B2 and Sonos's off, wait a while and power the Sonos's on again. Wait for them to connect to WiFi and then power the B2 on.
Paul
Brennan Support.