Hello,
It happens a lot that I summon Thorn Totems and during a fight I notice that they do not shoot at all.
Far as I saw, I think the reason is that a new enemy is either spawned after totems were summoned. Or enemies just was not on the screen during summoning and come later in combat.
Also it seems that Thorn totem attacks can hit one target only once per it attack tick. I do not know if its intended but it is a reason why to avoid Skill tree nodes with lowering the arc of shooting completely.
Thank you