I was going through more feed than normal on two occasions this year...
1) Our feral flock of then 24 Guinea Fowl learned that there was a free all-you-can-eat buffet in the coop.
2) Several of our barn cats learned that there was a buffet in the coop.
It doesn't sound like you have Guineas, but it could be feral cats...
I've also experienced what HorseFeatherz NV mentioned about changing the feed and the hens digging through it to find the good stuff (often the cracked corn) and spilling the rest on the ground.
I've also heard that goats can be a problem (if you have goats?).
1) Our feral flock of then 24 Guinea Fowl learned that there was a free all-you-can-eat buffet in the coop.

2) Several of our barn cats learned that there was a buffet in the coop.

It doesn't sound like you have Guineas, but it could be feral cats...

