What you were expecting to happen, and what actually happened:
All green enemies (troops and hero’s with a weapon that uses green mana) to show a forest herb icon underneath, not just troops.
Currently only green troops show a forest herb underneath them on prebattle screen
How often does this happen? When did it begin happening?
Since start of Legends reborn
Steps to make it happen again
Go to pvp, fight a player who has a green weapon, observe no legends reborn item underneath hero on prebattle screen