The Scene_Trigger scene must already be on air. The trigger does not automatically put the scene on air.
So from sequencer, make sure the Scene_trigger is played first.. but in doing so, your IN scene director will already be "played" in the scene trigger, so sending play again won't do anything.
Change your trigger to "Play Range" from 0 to 20, and it will play again.
Or change your Scene_Trigger scene to not automatically play the IN scene director when it goes on air.
#XPression