Can you take a picture and post it?

I would check to be sure moisture is actually reaching the roots. If the potting mix was left on the roots when you planted them, it may have dried out and since most growers use a peat based mix, once it becomes dry, it is difficult to get it saturated again.
Rb

OR could be just planting stress...July is not the best time of year for planting and the outer leaves just got stressed and are dying off. I'd cut them off with a clean pair of scissors and then baby the green parts that are left. don't fertilize though... fertilizing a stressed plant just makes things worse.

Had the same thing happen to me. Planted 5 coral bells (a few different kind)last spring. One dried up in the fall but came back this spring. Now that same one AND another one (different type) both dried up. All got the same water, same soil, etc. The only difference is a slight difference in amount of sun but I can't blame it on the sun because the 2 that dried up are in different sun levels. Oh well, as long as both come back next spring. I was just looking forward to the beautiful colors this fall.

Heuchaera is prone to crown rot. Most likely getting too much water, and too much humidity rather than not enough. Some heuchera are more prone to it than others. I've found 'palace purple' and 'caramel' to be pretty resistant, while 'creme brule' seems to flop and die no matter how many times I try.

I agree with carrieb; it sounds like crown rot. However, if the plants are a few years old they may benefit from dividing in the late Fall or early Spring. Good luck.