Q: What’s eating my hostas? Any suggestions? What can I do to stop it?
A: I think you have two problems. In my experience, when a creature eats a leaf, the edges of the damage are clean. There is little dieback from the damaged area because no fungus has been introduced. That’s the case with several of your leaves. I think slugs or snails did the deed.
On the other hand, diseased leaves usually have brown tissue surrounded by an irregular margin. The initial infection grows outward and brown or yellow sick tissue typically surrounds the original damage That seems to be the case on a couple of your leaves.
I recommend you read this to get insight on slug and snail control. Then fertilize with Milorganite or Holly Tone to boost the growth of the hosta and help them produce more healthy leaves.