Do you have video of this happening?
I am able to activate it just fine, so long as I actually hit an enemy. It might be the specific enemy you're hitting that's failing to activate it.
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But it doesn't SAY it has to hit an enemy. The description of the exotic perk specifically states that "activating" an arc melee should proc cross counter, but it requires that the uppercut make contact with an enemy to work. This would be acceptable if it weren't consumed when you miss, like a shoulder charge, but either make the perk work as described or change the wording to make sense.
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The description on the perk could be clearer, but it's working as intended. Punching the air with the other two subclasses doesn't activate it, so it goes to reason that using Tempest Strike and hitting no enemies wouldn't either.