Same question as found in a post over 1 year ago, yet no replies and over 143 views. Can anyone provide an answer? (hello, Sonos support?). I’ve searched forums and have not found similar issues, questions, etc.

In the Sonos app (Mac desktop), under 'Group Rooms' and 'Select rooms to group', what is the difference between a groups box that has a white checkmark with a blue fill background and a black checkmark with a white fill background? Upon initial selection, all boxes have white checkmark on blue box. At some point, the boxes on select groups (typically the same groups of speakers) will change to black checkmarks in white boxes. Frequently, but not always, the speakers in the group with the black checkmark in white boxes will no longer play.