Has it been confirmed what AoA sensors were fitted?
Pretty likely the Thales C16291AA given the choice of Pitot tube, if so one could have been suffering an extreme variation of the known fault at low temperature:-
EASA Airworthiness Directive
Note that the use of 3 sensors means that a single failure can be accommodated - but surely there should eventually be an ACARS maintenance warning to get the probe looked at?