Grasshoppers? Slugs? JB's?
Looks like it could be either slugs or JBs or both. I normally have slug damage on my hostas but this year I sprinkled crushed eggshells around them as soon as they poked up through the soil. This year: zero slug damage. They've never bothered any of my heuchera though and I have close to a dozen plants.
If I were to find sharp notches from outer edges leading in, in my climate it would be weevil. Go out after dark with a flashlight, look. You may have to make more than one trip, begin about dusk and if you don't see anything, try again later.
I do use Sluggo regularly and I don't see evidence of slug damage.
The notches are all from the outer edges so maybe weevils. I never had this damage before and they've been in the ground for 4 years now!
On a side note, it looks like your 'Jack Frost' brunnera may have foliar nematodes. And I'd agree with the weevil damage on the heuchera.
It's weevil time. Overnight all of my Rhodies, huecheras and Clematis have weevil damage.
I think every brunnera out there has foliar nematodes. As much as I like them, I'm about to pitch them all and not grow brunnera any more. They look nice in spring, but by July they are ragged and look like crap.
Is the damage new? If not, maybe it's winter moth larvae. One of my heuchera was decimated before I noticed the caterpillars. After that I started checking all the heuchera and hand-picking. But this was back in late May/early June.
I get lots of slugs and snails in my garden but they've never so much as taken a nibble out of any of my heucheras.