It looks like reinforcements are hard coded for that location-either by time, or threat. The AI should not have been able to move into there without a battle occuring. Although there is now a vacant province, it is still marked as under German control. That province was ocupied until the May movement.
I am wondering; is this WAD?
If it is, then I need some info before I can proceed.
1. Will those surrounded French units be supplied? The fortress is still intac.
2. If they are considered supplied, then will/can Verdun become a supply base as those surrounded units begin a conquest of Germany?
The attached file shows the whole Western Front in the political mode. Verdun is right in the middle of it with a stack of corps reaching for the moon

I'm using the 105 beta patch.