Hi,
This bug happens on a 11.31 that I compiled myself (and Pak128.Britain-Ex-0.9.1 but it shouldn't be relevant here). I'm not sure how I can provide you with the github branch I used... where do I find this information?
Anyway, trying to understand how supply and demand work, I sent a few loaded convoy straight to the depot, which lead to their load being counted as "In Transit" forever, unless I save the game and reload it... which then stuck my factories, roads, and so on.
Hmm - I have tried and failed to reproduce this, I am afraid. Can you give any more detail as to the steps necessary to reproduce this reliably?