Very strange. If the leaves are indeed being eaten off the possible culprits include grasshoppers, caterpillars (look in the surface inch of soil around the plants as many are nocturnal and stay in the soil during the day), or perhaps a beetle. You need to find out what is doing it for us to prescribe the correct remedy. Try also going out with a flashlight at night as this may help you catch the guilty part in the act.
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