There is a comment on another forum that uncommanded rudder is suspected.
Aaah, so that's why some posters ([3, 5[) have mumbled about rudder trim and stuff like that.
Well, I have been following this discussion here and no, only for those rudder trim guys noone have mentioned such gossip. But sure, this is for rumours too, as it says in the title.
Uncommanded rudder scenarios happened on a few Boeing 737's many many years ago. Hydraulic parts froze at altitude and when hot hydraulic fluid entered the part it jammed and caused a rudder hardover and even rudder reversal.
However all the scenarios where this happened were uneventful flights where the rudder all of a sudden slammed to one side and the plane nosedived straight into the ground. We are not looking at that kind of scenario here.