Probably nocturnal beetles of some type; see info and pictures below for more info:

https://www.americancamellias.com/care-culture-resources/insects-and-diseases/leaf-eating-pests

You may want to take pictures on different days and from the same location/angle, to see if the damage appears to continue (which means the pest is still around) or appears unchanged (which means the pest may have left).

I have never used Sevin because some people told me to not to try it due to having pooches. Neem oil will reduce feeding on your plants. The pyrethrin kills the pest and is said to be safe enough to spray even on food crops. But a systemic insecticide like Merit is an option.I hope this helps.

It is not bad for the plant at all. Foliage of any naturally occurring species gets munched all the time by various insects with few, if any, ill effects. It is more a cosmetic or aesthetic issue than anything to be concerned about. I have a high tolerance for leaf disfigurement on most plants as the cure is typically worse than the problem, as most insecticides - and certainly Sevin - will kill off the natural predators and other beneficial as well. I prefer to let nature take its course :-))