I suspect you had a critter feeding on the roots.
I would not dig it....but I would add about 1/2 a cup of alfalfa meal, cover the roots with compost....but before you do that dump in a few moth balls.
I don't think you will gain a thing by digging it but to view damaged roots....you now want those crowns to grow more roots.
Linda C

Thanks Linda - what has come up looks healthy, it is just much smaller than what I had expected of it this year. I did already cover the roots, so I think I may let it be so as not to bother it further. Unless it starts showing signs of not growing well now that the roots are covered back up.

What does the alfalfa meal do?

Alfalfa pellets contain a plant hormone, as well as nitrogen and phosphorus which stimulated plant growth.
Try it....it's amazing.
Linda C

But alfalfa attracts chipmunks and other rodents... do the moth balls mitigate that, Linda?

Would it not be worthwhile to dig up the hosta, see what is going on with the roots and replant? I had a Sum and Substance that was attacked by voles and there was a tunnel right under the S & S. Would it not be good to replant and therefore place soil back where the tunnel is (if one exists)? If no tunnel, no big deal, just replant the hosta. If it is voles, would they not make a return visit?

After reading Dmid's post, I may have voles on the brain. It does not sound like a vole problem.