You may have lost the connection to a Call Bridge, or it may have been turned off. There is a delay of up to 5 minutes before Meeting Management registers that connection to a Call Bridge is lost.
However, you will notice that you get errors when you try to make changes to meetings that are running on a Call Bridge that is disconnected.
Also, some video systems may not support the specific layout you have chosen. See also: How will my endpoint layout controls behave when used with Cisco Meeting Server and managed by Cisco Meeting Management
And some video systems do not support that you unmute a participant from Meeting Management. See also: How wil my endpoint mute/unmute controls behave when used with Cisco Meeting Server and managed by Cisco Meting Management?