Missing hinge?
This is really a question: How many hinge brackets are there holding the A310 rudder? The photos I'm seeing of the Air Transat fin suggest that there should be another bracket attached near the top of the fin/rudder. Did this top bracket get carried away when the rudder departed? If so, it could have been loose on the fin to begin with, and that looseless permitted flutter to develop, which precipitated the loss of rudder.
Again, this is speculative - I DO NOT KNOW how many A310 hinge brackets should be there. Details welcome.
(Ever read Gann's "Fate Is The Hunter" with the DC-4 elevator unporting episode?)