Have you checked for cutworms? They come out after dark, and are a recurring nuisance in my garden. They eat both leaves and flowers in my case, but seem to prefer flower buds. That damage in your photo looks a bit like the cutworm activity on my plants. The tricky thing about catching cutworms is that when they sense any vibration, they drop off the plant. So you have to sneak up on them. On the ground they look like a stick, and they are extremely good at hiding during the day. Good luck! Mike