I'm not sure if this is a bug or if it's intended behavior. I've noticed that the only way to reliably get scenarios to happen at installations and megaships is when there is a war or civil war in the system. When there is a war the scenario is always attack/defend.
Sometimes I've seen scenarios at installations with no war or civil war in the system and then it's usually the heist scenario. It's pretty rare to get scenarios without the war or civil war though.
Sometimes I've seen scenarios at installations with no war or civil war in the system and then it's usually the heist scenario. It's pretty rare to get scenarios without the war or civil war though.