Those holes could be appearing at different times, so I do not think it is frost damage. I also noticed there was some poo left on the leaves nearby ( not sure if it is related or not ), so high probability of some insect damage as I am not sure if slugs leave a poo afterwards. I saw some wasps visiting, but I am not sure if they are more interested in sweet secretions or ants... Lily beetles? but I did not see them on peonies so far. Mystery... May be frost after all, I hope so...
