This looks like abiotic damage, which means it was caused by environmental factors and not a pest or disease. In this case, it looks like sunscorch (also called sunscald or just "scorch"), which is essentially sunburn. Plants with reduced air circulation, such as being crowded or growing near a wall, solid fence, or near heat-reflective pavement or stones can be more vulnerable to scorch, but even well-spaced and unobstructed plants can still develop it. Beans can be among the more vulnerable veggies to scorch.

Fortunately, mild scorch in beans generally does not affect yield. You can keep monitoring the plants for watering needs, feeling the soil a few inches down and watering if it becomes somewhat dry to the touch, but no other intervention is needed. Floating row cover and insect mesh netting can serve as a shade cloth of sorts (even if not needed for their pest-excluding or frost-shielding properties) if a full sun exposure is proving to be too much for certain plants, but we'd expect these plants will grow out of it well enough on their own. (Injured leaves cannot heal, but new foliage should emerge normally.)

Miri

Glad to hear this. Thanks, Miri!

You're welcome!