Hi. It is impossible to know for certain what is causing the damage without seeing the culprit in action, but I suspect you are dealing with slugs, which are notorious pests of hostas and many other perennials. This page from Michigan State U. lists the most common pests of hostas, and the damage in your photo most closely matches that caused by slugs. You can download a detailed PDF on hosta pests and diseases here (from Iowa State and other universities), and the damage shown on p. 12 is a good match for the photo you sent. This page from the U. of Minnesota discusses slugs in home gardens and various things you can do to control them. There are some cultural strategies you can use, such as thinning leaves and minimizing excess water (to the extent you can). You can also use traps; putting beer in a shallow container can be very effective for decreasing slugs populations (details are described in the PDF). Boxelder bugs feed on trees (especially boxelders and maples), so even though they are in your landscape, you don’t have to worry about them damaging your perennials. This page from the U. of Wisconsin briefly describes their lifecycle. Similarly, chinch bugs are pests of turf grasses (lawns) but not perennials such as hostas. Ohio State U. has a page on their biology and management here that you might find useful.