UPD. tested in Wrotgar, Morrowind, and Glenubra, only mages, nobles and warriors are looted, no other miserable containers. Almost-zero drop rate of high-quality items, and enormous amount of white and green treasures.
Do you have a source for the claim that Treasure Hunter affects loot from stealing? After all, the passive says that it "Increases the quality of items you find in treasure chests", and doesn't mention thieving.
Do you have Legerdemain maxed out? That is what affects the quality of loot you get from theft, not Treasure Hunter.
7-day PVP campaign regular 2016-2019, Flawless Conqueror. MagDK/stamplar/stamwarden/mageblade. Requiem, Legend, Knights of Daggerfall. Currently retired from the wars; waiting on performance improvements.
Check if you have the passif. It's work fine for me since the maj in chest. Purple item in simple chest, it's okay.
What the..?! Been using treasure hunter passive for about a year now, and I never got any purple item in a simple chest. Well, like it matters what color when it's training or prosperous. Ha ha. Well, now that invigorating has seemingly replaced prosperous, I'm not too sure about invigorating either.