Dec 10, 1942. All of a sudden, my trucks went -30K and are staying there. I cant think of a reason why this is happening. Is it related to building infantry corps or something else. I have been attacking the whole time.
In my experence, apart from the units built it is mostly goverened by weather and distance to railheads. Blizzard will cause a truck drop, as well as advancing from your railheads, and these often come at the same time.