Occasionally during games of showdown, either me or my teammates (I've noticed this with the enemy team once as well) will die, and then be unable to respawn naturally, having to be revived in order to rejoin the fight. I do not know what causes this, and my only clue might perhaps be hitting the "interact" button (or whatever button makes you respawn manually before forced respawn in game modes like gambit) to respawn when the timer hits 0.