Try using an acidic fertilizer. The concrete wall is alkaline and hollies like acidic soil. Hollytone or something else designed for acid loving plants. Once they start looking healthy again and you start seeing suckers, I'd shear then back real hard so that they'd fill in to create a dense bushy plant.

I also would likely give them some additional water at the base from something like soaker hoses. They don’t require wetlands, but often occur there in the wild, and since we are in a borderline drought situation in many parts of New England now, they may be feeling a bit water stressed.

I think they look very good actually. An unfortunate attribute of inkberries is that they do develop exposed trunks at the base, not enough to matter in most landscapes but you've got them on top of a wall where you're looking right up under their skirts.

Thanks everyone for your advice! I do have one follow up question - we have two other inkberry hedges in our landscape that look the same, health wise, as the one I posted. Each hedge is made up of 4 inkberry plants and they are (supposed to be) mirror images of each other on each side of our front door. When the landscaper planted them, he didn't do a very good job of measuring and one of the hedges is noticeably off center. Would you advise to just leave them, or should they do okay if we dig up one of the the hedges and shift them about a foot to the right? Just wondering if inkberrys typically do okay being replanted after being established for about 2 years?

I haven't tried transplanting inkberry, but it will probably be OK--just don't do it now during a heatwave! October would probably be a good time to do it.