Surprised nobody picked it up, same thing happened to a 757 freighter in 2014, it was updated on AVH yesterday:
A Yakutia Airlines Boeing 757-200 freighter, registration VQ-BPY performing flight R3-9990 from Magadan to Yakutsk (Russia), was climbing out of Magadan when the crew stopped the climb at 2000 meters due to the forward cargo door opening.
The incident was blamed on ice/snow blocking/freezing the latches. That may well have been the case with DHL too with he current cold spell in Europe.