Sometimes, when queueing large orders (it usually happens to me with berry sludge, but has recently also happened with a steel order) the last order in the queue won't produce an errand. The building will still have a recipe queued (always only 1), but the errand list will be empty. The building won't say that it's missing materials, and often will already have all the materials needed. It can be fixed by emptying the storage or by removing and re-adding the order.
I'm not sure exactly how to reproduce the bug. It happens to me relatively often, usually when I queue 10-20 berry sludge orders at once.