If it stayed on the spit too long you'll get coal instead of cooked meat. If your fire pit is not on level ground the meat can roll under or away from it. If you stand in the fire you'll take damage unless you have troll or better armor in which case your fire and the cooking spit (and cauldron) will break.

You can solve this problem by using your hoe to raise/flatten the ground just a bit so the meat goes into your inventory instead of on the floor.