I understand that the fix was to add tail feathers.
Wallis added a tailplane ( based upon the Spitfire's tailplane outline) post the resultant reports generated by the Farnborough accident.( he also added one to "Little Nellie" IIRC) .Later on he also added very small canards to the nose at slight negative incidence to help keep it down when flying fast under max power for the speed records. He reckoned that that was "the solution" . I'm not qualified to comment on that.