Ah, the good ole inventory spill. Well, at least spilled items don't drop onto belts anymore, clogging the entire factory.

Cause: Either..

• You were crafting something with a lot of ingredients, and picked up more ingredients during. Then crafting was canceled and there wasn't enough room for all the ingredients.
• Your inventory capacity was reduced, mostly likely by removing armor with an inventory capacity bonus.

The fix: Either..

• Run over and hit the "pick up item in ground"-key. I think it's F by default.
• Select the items in ground with a deconstruction planner and let bots take care of it. You can create a deconstruction planner and edit it to only whitelist items in ground - It's by far the easiest. If you don't have bots yet, iirc if you run over an item on ground that is marked for deconstruction you pick it up automatically.