Tried out one of the side quests where there was an objective was to grab a key before being able to open strongboxes.

I do not know if it is planned or feature/bug, but will there be an option even after the "boss/unique" is defeated to allow party to continue scenario?

Annotated we defeated the end "unique" and the scenario ended immediately.

It did not say in the rules page, but for this case as most of the instances are not a normal search function on a normal turn. Why isn't the party able to go back to those items after retrieving the key and defeating the monster? Or why aren't other remaining monsters suddenly charging from the rear all of a sudden going to give up especially not being a "timed scenario".

Tried out one of the side quests where there was an objective was to grab a key before being able to open strongboxes.

I do not know if it is planned or feature/bug, but will there be an option even after the "boss/unique" is defeated to allow party to continue scenario?

Annotated we defeated the end "unique" and the scenario ended immediately.

It did not say in the rules page, but for this case as most of the instances are not a normal search function on a normal turn. Why isn't the party able to go back to those items after retrieving the key and defeating the monster? Or why aren't other remaining monsters suddenly charging from the rear all of a sudden going to give up especially not being a "timed scenario".

This quest has two distincts win conditions after you got the key, or defeat the unique boss or catch all treasures in the room (the locked ones).