if i understood corretly valkynic
if u lure mobs by passing them (auto agro) or by pulling some mob next to u, the mob group is not casting skills, but if u hit them or agro them, they cast skills - in this case stun. If u have reflect every hit from mob normal attack is considered as u hit them back so they start use skills. And skills stun, when u dont have reflect u dont "hit them" and there may be only 1 mob using stun, not many thats why not land so often.