Does that sync group used for redundant (same content) or stacked mode (more than 24channels)?
How did you set up the sync group? Is there any router, switch between?
However.. the Master goes into the normal stand by mode but the Slave transport buttons
flash and then the Stop / Play / Record buttons all light up
Where you seen this does the “M” and “S” at the top of the display are solid or blinking?