What you were expecting to happen, and what actually happened:
I was expecting a Firestorm to start the battle with Rubirath in 3rd position, but the battles started with Essencia’s Lightstorm or Stringfiddler’s Leafstorm.
How often does this happen? When did it begin happening?
It happens every time I enter an Explore battle with this troop arrangement.
Steps to make it happen again
Enter any explore battle with duplicate troops (Rubirath in this case) that start a storm in positions 1 and 3. Place a different troop in position 2 that also starts a storm at the beginning of battle. The troop in position 2 will dictate the storm that starts the battle.
Not sure if working as intended, but since the “third” troop is essencially the first troop share these traits once so it counts the very first one position troop traits.
And then start to count any other different troop, like in this case Essencia Lightstorm