When i hover over the icon to show what will stun an Unstoppable enemy and break it's shields, one of the things listed is solar ignition. Both my grenade and melee ability have the ignition effect but aren't breaking their shields. I've tried it multiple times, only way the icon even lights up in my character menu as solar class is if i equip a scout rifle. But if i don't have one equipped, the icon isn't lit up and ignition isn't doing what it's supposed to be doing.