I saw this train come in 'live' on the webcam and it was hauled by one of the shunters and there was a man on the back on the last wagon. So it must come from the Plattling paper factory / Plattling sugar factory or Deggendorf Port. It can't have come from Vilshofen as that is too far for one of the men to stand on the back of the wagon for so long. The white vans have writing on them but I can't make out what it says. It only arrives in Platting on a Monday at around 11:15 (German time).
*edit* on Google Maps, it looks like the same white vans are found at Plattling Sugar Factory
https://www.google.co.uk/maps/place/94447+Plattling,+Germany/@48.7865673,12.8805355,184m/data=!3m1!1e3!4m5!3m4!1s0x47750dbb9cce56d9:0x3e8be490276de975!8m2!3d48.7806071!4d12.8690362
https://www.google.co.uk/maps/place/94447+Plattling,+Germany/@48.7863375,12.8756587,390a,20y,90h,41.53t/data=!3m1!1e3!4m5!3m4!1s0x47750dbb9cce56d9:0x3e8be490276de975!8m2!3d48.7806071!4d12.8690362
http://www.suedzucker.de/en/Unternehmen/Standorte/Zuckerfabriken-Deutschland/Werk-Plattling/