Here is the setup.  Five Sonos One V3 speakers, one Arc Soundbar + Sub Woofer

The condition:  I start playing music (Pandora) using either the Sonos ios app or using Google Assistant, i.e. “Play Pandora music”  If in the Sonos app all devices had been selected before starting the music all is fine and music plays throughout the house. 

I later stop playing Pandora i.e.  “OK Google, stop the music” 

 Later when I turn on the TV (connected to the soundbar via HDMI ARC), all is fine and TV audio plays correctly though the soundbar.   The problem is when you turn off the TV, the soundbar will not re-connect to the rest of the speakers in it’s group.  You must manually open the Sonos app to reconnect it to the other speakers.  The soundbar does have a selectable settings under “Home Theater”.  The first setting, “TV Autoplay” does just that.  When the TV is turned on the soundbar automatically connects to the TV.  The second option is  “ungroup on autoplay”.  This prevents the TV audio from playing though out the house on the speakers in other rooms.  Both of these options work as designed. 

The issue is there is no option to “reconnect the soundbar to previous settings” when the TV is turned off.  If you go back to the Sonos app or using Google Assistant to again play music  the soundbar is not part of the group and must be manually re-associated with the group.  I’ve suggested a third soundbar setting, something like “reconnect soundbar to previous group on TV disconnect”.   

I can’t believe I’m the only one who has experienced this.  If there is an option or setting I’m missing, I would welcome the ideas.  So far, Sonos support says that’s just the way it is.