It feels to me like Air France Flight 447 [0] - there was a flight computer behavior that the pilots didn't know about, but nonetheless following normal procedures would have prevented the crash. (For AF 447 that would have been "point the nose down to recover from a stall", for Lion Air 610 it was "check the trim wheel - you know, that thing that moves right by your knee - if pitch control is abnormal") Unfortunately, as we add more and more safety systems to planes people seem to be forgetting how to compensate for when the systems fail...

0: https://en.wikipedia.org/wiki/Air_France_Flight_447