Nitpick: “This event happens” is not in the passive voice. “This event is triggered” is in the passive voice — and so is “this event is triggered by subsystem A

Nitpick: “This event happens” is not in the passive voice. “This event is triggered” is in the passive voice — and so is “this event is triggered by subsystem A”. (What you probably mean is “writing something vague or lacking agency”.)