Xilith I can pretty regularly reproduce by zoning and watching my combat log. When I zone, upon entering the new zone, my combat log states "You relax your stance." When this happens, my stance bar still shows me in my stance, and my buff bar still shows my stance as applied, but I do not generate Vengeance. When I cycle stances, Vengeance will start to generate.
Here's a fun twist that I tried just now - I'm in Night Harbor with Offensive stance on. I toggle it off manually. Combat log states "You relax your stance" and all visual cues (stance bar and buff bar) show I'm not in a stance. I zone to Shaded Dunes. No "relax stance" message on entering new zone. I am automatically placed in Offensive Stance. No combat log entry about going into Offensive Stance. Enter combat, still cannot generate vengeance. Shift stance mid-combat. Start generating vengeance.
If I had to guess, it has to do with some kind of state transfer of the characters, whether between zones or from a "logged out" to a "logged in" state.
Happy to stream this or something if it's helpful.
EDIT: You will note in Jeembo's video, the "you relax your stance" is present when they zone as well.
