I encountered a similar (but different) bug and reported it at Patient died & flight terminated after "Skip to Next Phase" In that bug, the plane successfully got to 31,000 cruising altitude, and that “get to 31” task was completed (checked-off) okay. I even completed the “keep plane stable during checkup on the patient” task, and that task was checked off okay. In that other bug, the “Mission Failed” event happened later when I attempted a “Skip to Next Phase” action.