Have you actually checked soil moisture by sticking your finger down in the soil a few inches? You might have voles or other critters that have tunneled under the plants so the water runs away down the tunnels. To me it looks most like a water issue.

However, is there a chance of weed and feed or other herbicide coming in contact with these plants, perhaps even from the other side of the fence?

Did you use landscape fabric or plastic under the mulch? That can interfere with water movement in the soil.

We had a mole, no plastic, just weird cause other plants in that area are fine...thanks NHbabs!

I agree with the thought about water shortage.

On the other hand, root rot makes plants appear very similar.

Advisable to poke around and look at both soil & roots.

Looks like it needs water to me too.