I know it did not happen on any Frantic escort missions from UK to Russia to Italy and back.
I haven't found any reference of Soviet fighters 'escorting' 8th or 15th AF to Brux, Posnan or Ploesti.
Near the end of the war they may have been in same areas like Leipzig, Brux, Ploesti, etc but not on a planned basis - we had all the escort fighters we needed by the time the Soviets had their own fighters over those targets