Did you ever figure this out? Having same issue 

Hello,

Could you share some screenshots, please? I'd like to see the mission and the champions you equipped.

Got it today. three sets (pairs ) of 3-star ATK artifacts, on the same champion. So, all the Attack champion is equipped with is the red blade items in all 6 spaces. Yay!

That did not work for me. I put all 6 3star attack weapons on a 3 star champion. Still, no go.

Are they wearing all offense sets?

Is it an attack type champion?

if that fails, can you take a screenshot of your gearing, thanks.

Does it mean three sets of pairs? Because this is theee of offense. and if that's the case why not just say all offense 3*? This is the second champion I've tried to do this with. I've managed to get 1/3 from another champion I tried it with so I'll try pairs next I guess  

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FOR ANYONE ELSE WHO COMES HERE:  Just make everything OFFENSE. It means three pairs= full set= 3 sets because 2x= a bonus I guess?

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