I've tried multiple times with all 8 red rreign wearable items in my inventory, refreshed the achievement, and still nothing. It won't even show up partially filled when I keep one or two of the items in my inventory. I've borrowed for this achievement so I've even treid sending the items back to their owner, keeping my owned ones in the inventory and then accepting the borrowed ones back, but it still won't go through.

have you tried putting it into your wardrobe? i'm not sure, but i really think it's odd that you are supposed to have it your inventory when most of those achievements are for the wardrobe.

I did ! I was wondering the same thing. I tried both in and out of wardrobe with refreshing etc and nothing. I own 3 of items and borrowed 5 and the owned 3 dont even show up

I did. I had it open and refreshed it multiple times over around 10+ minutes. I tried opening it in it's own tab as well to see if that would help and still nothing shows up.