I think many ppl didnt watch their older vids, hyejin not the only one who complained or showed dislike, there are times kota too, it's just it's not shown as many as hyejin, but they mentioned it here and there through out the 4 years of their vlogs. They are just NORMAL couple who banter for fun and tease each other, had a fight and still honest if they like or dont like something, that's better than keep it inside (as long as there is no actual physical/verbal abuse), especially if they will take this relationship to be more serious (marriage), they need to be more open.