Oh I think I stumbled across something like this : I clicked on waste, validated the activity, and then opened the crafting menu before my character arrived at the wastes. I chose to craft a rope, and the menu closed. The menu of waste found then opened (telling me I found plastic or whatever) and when I closed it, my character didn't go craft a rope. So I opened crafting menu again, selected rope, and they went to craft a rope, but crafted 2 instead !