The Score parameter in the Region inspector controls whether the selected track appears in the score. If the Score checkbox is unselected, the selected track is not displayed in the score. This lets you exclude certain tracks from the score display—for example, those that only contain MIDI events that can’t be displayed in the score, such as controller or SysEx data.
In the Region inspector, deselect the Score checkbox.
You may need to click the More disclosure triangle to see the Score checkbox.
Select the Score checkbox to have the tracks appear in the score display.