as you probably know events need certain triggers to happen for the event to fire for this event you need
trigger = {
exists = AUS
atwar = no
NOT = {
atwar = AUS # Austria is not at war
alliance = { country = AUS country = SOV }
alliance = { country = AUS country = ENG }
alliance = { country = AUS country = GER }
to not be at war with any nation during the time of anschluss austrai also must not be at war and you must not be allied with them or austrai must not be allied with england or the soviet union
but if its none of these i would try reinstalling the game and also there is a 1.3b if you didnt know