Thank you for the feedback :)
If I might ask, which of the four thieves did you fought in chapter 3 and in which difficulty were you playing on?
Fought two thieves, the one who shows up when the player partners up with Ox in their room and the one who shows up when partnering up with Tamara. For Ox, we failed slowly. For Tamara, it was instant kill for the player at the start and then Tamara died soon after. Statwise, was 2S 5A 2D 5I. Had like 6HP.