After looking at the JP translation, it seems like EN mistranslated intervene, intervene arent supposed to stun. sad. Like i personally tried to use intervene and harassing some people to the point where they run so far away i get to 1 v 1 them and intervene just never stun them even they arent on a class with stun prevention outside of purify. So it has to be a mistranslation, and I doubt it's a bug at this point.