This is an issue I am having on my Invulnerability/Super Strength Tanker.
Not sure what's causing this, but when I am sync'd to lower level (so far have seen this through levels 1-19), my single target abilities are not triggering the AoE taunt from Gauntlet. The taunt aura provided by Invincibility however, works as normal. I also get a message in the combat log saying "You cannot use Gauntlet when you are fighting at level x."