Besides slugs and snails, foliage feeding caterpillars, cutworm larvae, and earwigs can chew on hosta and iris.  Earwigs are omnivores that mostly eat dead and decaying plant and animal matter, and as a predator, aphids, maggots, cutworm larvae, & insect eggs. However, they can also chew on live plants. Here is some information regarding management of earwigs from the Pacific NW Insect Management Handbook - https://pnwhandbooks.org/insect/structural-health/nuisance-household/nuisance-household-earwig       

Weevil could also be the culprit if leaf edges have irregular notches. Here is some information from the PNW Insect Management Handbook - https://pnwhandbooks.org/insect/hort/nursery/common/nursery-crop-weevil

The best way to find the culprits is to do some night time investigation - that is the most likely time they'll be out feeding on your hostas and irises.  If you see slime trails, think slugs and snails.  They may have found an avenue to your plants through the broken filbert shells although I've found them to be a pretty good deterrent also.   You may need to consider some beer traps or bait use if you discover slugs and/or snails.