Looks like something's eating them to me. Whatever it is, they'll soon be going dormant for the winter anyhow. They'll come back next year more than likely. I get a fungal thing in some of mine next to a stream that defoliates them completely in late summer each year, and they always come back the next a strong as ever. Next year you can spray them with whatever repels whatever's eating at them (slugs, rabbits, deer). Hostas are candy for lots of critters.

do you have deer? Mine get eaten by deer (and rabbits)...

slugs usually go for hostas, but that would have to be a BIG slug....

Carrie

Post over on the Hosta forum. Those nuts love looking at pics and will probably have a whole range of opinions/ideas.

Looks like foliar nematodes to me

I agree with brenda. A systemic treatment added now while you still have some leaf will help. Another treatment in spring after the shoots begin to open should help although it won't deter rabbit/deer browsing.
You might also want to check for vole activity. If you have them and they've chewed off much of the roots the plant will stop producing leaves while it grows more root system.
You can lift these plants to check for pest activity and replant them. Use a spading fork to loosen the soil and lift the plants so you can check the roots.