You’ve got squirrels (or other rodents). To protect the corms that are left, try covering the area with hardware cloth (they can grow thru it but the critters can’t get the corm out). You don’t want to smash the leaves, which are helping feed next year’s flowers, so wait until they start to die. Then you can cover the hardware cloth with a layer of soil, so it doesn’t show. Might want to put in some more corms if the squirrels have been at it for awhile.