I have noticed on TSW3, despite I am subscribed to several freight cars - for both Germany and USA - they do not appears when running timetables. No problem with locomotives, which appears for both my train and AI ones. Please notice I saw them in TSW2. Only exception are the JNA freight cars. They never appeared!. So it seems to be a TSW3 issue now about the freight cars. Hopes this be fixed too!.
I have also never seen any custom liveries appear for any of the freight wagons on either CJP or SEHS as well (don't have the German route). However, you do say that your loco liveries are working on CJP? I only ask because I have never seen a custom loco livery appear on any of the AI services or static displays on CJP, nothing at all, unless I select one myself and then it is always just that one single unit that I am driving. So maybe it is working, but not on every platform? I am on Series S. Incidentally, the 66, 395, and 465 custom liveries seem to show up just fine on SEHS
Same issue that many TSW2 routes had as well. Kind of takes away the point of custom liveries if they newer even spawn...