What in the world is causing this?

I have two Long Slim Cayenne plants in an swc, planted a little over a month ago - they were both healthy and the same size at the time. As you can see, the one in the back now is healthy and growing well, 3X the size of the deformed one in the front.

Since they're growing in the same container etc and the one plant is healthy, I'm having a hard time believing it's a nutrient deficiency.

I've checked it for aphids, sprayed it w/ some soap & water based organic insecticides in case its a pest I'm not seeing, but nothing has helped. I have 3 other identical scw's growing a total of six more pepper plants right next to this one, and they look excellent. So that's 7 healthy vibrant plants, planted identical conditions, looking great, and then there's this deformed one.

I'm debating just pulling this one out, and sticking another one in its place. Its a little late in the season to do that here in Ohio, but I'm not sure this plant is going to recover.

Any advice?