Clematis roots don't really need shade; they need even moisture. Is this a newly planted clematis? Or did something do some digging around the base? The soil looks disturbed. You say lots of new growth around the top and bottom, but none of the photos show the top - can you add a photo that shows them top to bottom?

With the info given, I'd guess that something damaged the stem lower down on some stems, causing everything above the damage on that stem to start looking unhappy. If it's newly planted, you can cut them back to a couple of pairs of buds per stem to encourage multiple stems to grow. If the damage is restricted to certain stems, cut the sad looking stems down to where they look healthy. If they've been there a while I'd try to figure out what caused the soil to look disturbed. I'd also probably add some additional mulch to within a couple of inches of the stems.

They have been there about a month. I just dug around the top and amended the soil a bit yesterday. Here is the full shot.

Since it is newly planted, and new growth looks healthy while the long stems are struggling a bit, I'd just chop off the taller stems which will encourage more new stems to grow. You will have a fuller plant next year.

Chop them off about a foot above the soil. This will encourage more branching. You do not want to keep that lone tall scraggly vine. Did you plant deep? They should be planted 4" deeper than nursery pot. The rocks aren't necessary.