I've had this happen at least twice now in Competitive Brawl. Amalia is my commander. It happens when Amalia enters the battlefield, I have a life gain trigger (Soul Warden or similar), Amalia triggers off life gain and in response to Amalia's trigger (explore whenever you gain life) she becomes targeted by my opponent's bounce spell (unsummon or similar) at which point her Ward cost goes on the stack. Opponent pays the ward cost, I choose to return Amalia to my hand (instead of the command zone), and then the stack just empties / clears without resolving the explore whatsoever. The explore effect fizzles and that's that?