Remember, we're dealing with the people who invented the First ICBM's( V-1, V-2 ). The First Operationally, fielded jet fighter, ( Me 262 ). The First Stealth Fighter, ( Horton 229 ). AND designed the First Intercontinental Bomber ( Horton 18 ), both Flying Wing configurations. If anyone could make a train disappear it would be the Germans.
Just because it is not where we think it should be, doesn't mean it isn't there. Personally I think it is a Munitions Train.