Army Group Vistula were intended, in Guderian's mind, to be commanded by Field Marshal Freiherr von Weichs. "At the time he was just the man for this job", Guderian said.
But the Führer considered von Weichs to old, and Jodl maded some "remarks about his religious feelings".
"Then", thundered Guderian, "whom did we get? Hitler appointed Himmler! Of all people - Himmler!"Under Himmler, without any experience commanding troops at the field, the front began to collapse.
At that time, Himmler was Minister of Interior, Chief of Gestapo, head of the SS and commander of the Training Army.
After an agreement with Himmler, Guderian suggested to the Führer to relieve the "overburdened" Reichführer from Army Group Vistula, and after strong reluctance, Hitler agreed.
Main source: C. R. The last battle. 1966.