After all the excellent information about duplex bearings and preload offsets , we are still left to find a reason for the bearing failure and the excess torque on the spider end nut.
Unless the split pin at the spider end had come adrift, the control rod can't have rotated relative to the nut to tighten it - is the initial report wrong when it says that the torque is a result of that rotation and if so, how?
Unless there is a clear explanation of that process you come to the conclusion that the nut had been overtightened either on assembly or during servicing. Whether that excess torque directly affected the operation of the duplex bearing or just exacerbated an existing problem with it is one of the questions the AAIB will hopefully answer.