There is more than one way that fillet can end in a point, as you have recently demonstrated. You need to learn what is appropriate for each case.
In general, don’t use the trim option if you don’t understand the implications of using that option. You can always trim surfaces later. You have complained repeatedly about surfaces disappearing. That’s what happens when you use the trim option. The base surfaces get trimmed. If you don’t want that don’t use that.
Sometimes you use the extend option and sometimes not. It depends if the fillet naturally comes to a point on its own or whether come to a point because some other surface cuts across it at a diagonal. In this case the untrimmed fillet itself doesn’t come to a point. It only looks pointed at both ends after each end is trimmed by another surface.
The above only applies to answering your question about “where fillet needs to go to a point”. If you apply it for some other purpose it may not work.