Try using
GetPlayerAuraBySpellID instead.
Replacing:
Lua Code:
AuraUtil.FindAuraByName("Defensive Stance", "player", "HELPFUL") -- AuraUtil.FindAuraByName("Defensive Stance", "player")
with
Lua Code:
GetPlayerAuraBySpellID(197690) -- That should be the buffID, if not you'll need to find it yourself.