I had 1 AA unit short of supply 3 provinces south of Danemark, I checked around and saw that ground was frozen so I suppose that with bad meteo the supply route can be closed or delayed enough to block supply.
Also if you 5 divisions are very close their supply will need the same way for all. One thing you learn rapidly when using using supplied units is not to use all the units at same time to not bottleneck the supplies after (Remind the 2 tons trucks in the manual)
Also if you 5 divisions are very close their supply will need the same way for all. One thing you learn rapidly when using using supplied units is not to use all the units at same time to not bottleneck the supplies after (Remind the 2 tons trucks in the manual)