I have learned the following from another European web group, but would stress that this is not official information.
Earlier in the same day another train had hit a car on a grade crossing. This had caused much disruption to the planned service, which was itself a special service with lots of extras. Trains were meeting at different places from those originally planned. It is possible that this may have been a contributory factor to the collision.
It also appears that the locomotive badly damaged in the crash was a visitor from another line.
I will pass on any official information when available.
Don Newing
Derbyshire, UK