WATABENCH another theory??
I worked on the 757 for a while and I remember being told a number of times that occaisionally after a long cruise and rapid decent that around part of the mechanism i.e. the girtbar locks, that frozen moisture can be present causing an obstruction to the mechanism. Paritcularly if you've had a "blowing" door - one were FastJet2K's sachets of sugar and/or stirrers got in the way of the door seal making the cavity within the door colder than usual. We were advised that should we suspect the door not disarmed after a first attempt to try again and then just 'crack' the door open and hope that we weren't flung to the other side of the apron byt the power assist!!!
I certainly know that the 757 disarm lever would ocaisionally be hell to try and move after a long luxor 6hrs - which does kind of support the freezing theories.......Thankfully never got to "fly" across an apron though!
P.s. FJ2K I believe the 757 also has the problem of debris around the gubbins down below.