I've run into this problem before but with a different plants! The tell is that you were checking during the day and didn't see anything. Also you are an attentive gardener so you were watering adequately and enough.
So what you do is get a flashlight and go out at night after dark. If you do this too early in the night you won't see it. Try to out around 1 AM, and then at 2 hour intervals. If you don't catch what's eating them in the day its a STRONG possibility that you are getting night predators instead. Particularly certain ones like earwigs you won't even see them during the day. But then you come out after dark and they are chewing things up with dozens of them all over 1 plant. This is 1 night pest, but there are others.
So you come out at night and start spraying them with a dishsoap and vinegar solution. The dishsoap clogs up their oxygen pores. But it takes a few tries.
*I want to hit on this idea; if its night pests you have to hit them more than once. You probably hit it maybe 3 times that night but at different hours. Then do that a few days and usually it will take care of it. They sometimes can be deterred with that slug-o stuff too.*
Another pest is wasps and yellow jackets. They'll come and chew up the leaves to take back to make their nests with them (during the day). They don't eat the leaves, so they can be sometimes not considered as being at fault because people know wasps eat meat and sugarwater mostly (for young). But their nests require a leaf material to make.
