@EA_David What I think happens is the armor of the enemy going to the next tier. I'm often confused by the armor of the enemy evolving during fights, makes me hesitate sometimes, thinking that he somehow popped a shield cell / bat or managed to do a very quick armor swap (when there are many deathboxes around).
I think the evolving armor feedback / behaviour could use a change. First of all, enemies should not see the effect of the armor evolving until the enemy actually starts recharging shields. Also, the color of the armor should remain the same after evolving until a recharge is performed, maybe even until charging goes past the full value of the old shield.