Wyvern melee cant stack rage on Rend

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I am using both the Rage gem (which is a suggested gem), and rage passives, and despite Rend being listed as a "melee" ability, it will not stack rage at all.

+1 I'm having the same issue. Rage 1 does nothing for Rend even though it is recommended.

Also any gem I put in Rend is darkened as if I don't meet requirements even though I do. So I'm not sure any support gems are working. I don't have enough to test it atm.