If you are able to use the shovel (assuming that also doesn't get softlocked [in which case, you may need to restart the game and hope your progress saves]), shovel up any and all cob cannons from your lawn.

You should officially be out of the softlock! However, the cob cannon sprites will remain on the lawn unfortunately, and any plant planted over them, while functional, will more than likely have some visual glitches as pictured here.