Totally a guess and I have never seen it on any of the plants you named, but the semi-circular notches sounds like what happens to volunteer seedling redbuds and roses around here - leaf cutter bees? I have euonymus as well and haven't seen damage on it while a redbud seedling nearby was riddled. Maybe they have a preferential leaf cutting pecking order?

Here is a link that might be useful: leafcutter bees

Take flashlight out and look at night. Suspect caterpillars.

If it were one of the larva called caterpillars you would see them because they do not, as a rule, move around much and they would be there during the day as well as at night. Slugs and snails would be out at night because they do not like the warm and dry daylight hours. Cutter bees would be around during the day and can be very visible.

kimmsr - What time does the night shift start? I checked the plants shortly after sunset - was that too early? Slugs seemed like the most likely explanation to me.