A rodent or more likely mama snail did that. I would still put out the snail bait. There have to be adults if there are hatchlings. Snails hatch every three weeks. I would also try to keep the area drier. One of the reasons I am not a fan of mulch or leaving a lot of leaves around are that the snails like to hide in that. A toad, chicken, or duck are good snail catchers. Unfortunately they like plants too. You can try the propped up board or yeast/beer trap, which should be able to attract large and even the small snails.
I go on snail hunts early in the morning while the dew is on the grass. There is more light to see them and they are usually still out and about. Once it gets past 9 am they have gone into hiding. Look between and under pots, under the mulch and on the sides of pots and in the drain holes of the pots. Lettuce leaves make good bait for a trap.
I am having trouble with the snail bait. It is attracting the rats. I just bought an new mouse trap. I hope it is smarter than the mouse/rat.