So I finally received a response. Standard type email claiming that adverse weather conditions caused the cancellation. However the skies were clear and winds minimal. There were also other flights leaving the airport around the same time so I'm not buying it. I checked weather conditions at the arrival airport and they were also fine.

Does anyone know where I can find historical flight arrival information for FRA? I would like to be able to show that if other flights were arriving FRA on the subject days around the subject time, their explanation is baloney and I am entitled to compensation under EU 261/2004 for the cancelled flights.