No stop orders are triggered outside regular trading hours. Only Stop Limit Orders trigger outside regular trading hours.
There is a reason for not triggering stop orders outside regular trading hours (Which is a very respectable reason). Sometimes the bid/offer spread outside RTH is so wide that your stop order can be triggered and sold at the bid for like $0.01 or $0.5, which is ridiculous and for sure you will complain to IB, so they reduce such overhead by completely disabling this.
You must always use Stop Limit (If you want your order to be triggered outside RTH).
By the way, this is the case for stocks only, in futures for example, IB (Based on order parameters which you set) triggers stop orders outside RTH normally.
If your case is different and you have stop orders which are not triggered properly during RTH, then in this case you need to speak to IB customer support.