The yellowing is at the far end on both rows, front of rows is fine.

I had the same problem with my black-eyes peas. Someone told me
not enough magnesium. So I water them with Epsom Salt. 1 Tbs. per
gallon.. At that time we were getting a lot of rain..In your picture you
cannot see the yellowing. You need to get more of a close-up.

Are the yellowed plants a different variety or just located in a different part of the garden?

If the variety is the same for all of them it must be a soil problem, maybe a nutrient deficiency. That could be a magnesium deficiency, as roper says, or even a nitrogen deficiency, unlikely as that may be for legumes. An oversupply of some nutrients which can prevent uptake of other nutrients even when there is a good supply in the soil. I wish I could be more specific, but that's about the best I can do.

Jim