Okay, I finally got it. The problem is that the window you have to get it from Tuon is insanely small. When you return from the desert temple you automatically rest and the next day the mailman ask you to deliver the letter to the commander upstairs. That's the only moment you have to get the armor. The moment you deliver the letter, Tuon despawns. I missed it because since you get the letter inside the Inn and have to deliver it upstairs, there's very little reason to go outside in that moment.
DigbyCrossing
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(Small spoilers ahead)
Maybe I'm missing something but the scene where Tuon pats your butt while wearing the slave outfit seems to be locked outside the gallery, since you can't get the outfit before heading down the mines. You need the cauldron to get the armor, but you can only do it after completing the jungle caverns that open the path to Bizz. Tuon leaves the settlement long before (by the time you are doing the delivery task he is already gone) and doesn't return until finishing the mines. That makes it impossible to see that exact scene outside of using the gallery. Giving him the tatters seems to do nothing in this update. He just keeps them, tells you to wait a little longer and then leaves after a few explorations.
Again, maybe I'm missing one exact point in the timeline where you can access Bizz before the jungle caverns, but I haven't found it yet.