refrig. not staying cole enough?

The refrigerator door does not hermetically close properly all the time. It doesn't appear to be a gasket problem. It's like if the pressure conditions in the fridge are good, there's a good seal and the door stays closed. Otherwise, when attempting to close the door, it bounces back and does not seal. I have to bungee cord it down so that it''ll saty sealed. Other than that the fridge works fine.