These days we would also think in terms of human factors:
Extreme cumulative fatigue of night bombing operations.
A possible loss of concentration due to stress release after crossing the home coast having "survived" another raid.
Possible loss of situational/altitude awareness during the landing checks.
The possibility of damage, known or unknown, to the aircraft causing difficulty lowering flaps/undercarriage distracting from "flying the aeroplane".
Loss of, or damage to, one or more engines due to enemy action or fuel shortage, or damage to the airframe causing handling difficulties.
The black hole effect of a probably remote rural home airfield in the blackout of wartime leading to a loss of altitude awareness.
The list of possible contributory factors is endless. We know that many of the enormous losses suffered by Bomber Command were other than by direct enemy action.