I doubt it is work of weevils, grasshoppers, or caterpillars. The leaf eating pattern is more consistent with night time beetles. Whatever species you might have. I have and had similar issue. You may never catch them red handed. They do the damage and next visit mighty only be after a month. My situation is slightly different because I have lots of other greenery around. Yours looks more urban area, so they might be due for more frequent visits. First two hours after dark is more favorable to catch them in action.