Flame Totem + Ice Shield?

I'm in Lunaris Temple fighting those critters that cast Ice Shield and are vulnerable to fire (at least some of them are). I'm using Flame Totems to try to kill them but their life simply never goes down. I even have 2 totems at the same time and their hp never goes down. I'm not using any other skills obviously.

Is this normal? The only way I've managed to kill some is when they hadn't cast their Ice Shield. My Flame Totems should be melting them either way. What is going on?