What about soil conditions? Are they planted in uniform soil, or is this one in a spot that drains better?
Is it more exposed to winds? Could the water be running off this particular plant?
Could this plant have been fertilized a little more, or differently than the rest?
Any root damage possible?
Physiologic leaf roll usually affects mostly the lower leaves. It's a way for the plants to reduce transpiration. So if the roots can't take up as much water as is being transpired out by the leaves, then the plant reacts by curling it's leaves.
Some thing can cause this but most of the time it's environmental. Too much high nitrogen fertilizer can cause too much top growth without an equal amount of root growth. =leaf roll
Temperate spring weather can cause a lot of top growth, and then when it gets hot hot hot, the roots aren't sufficient enough to keep up with the sudden increase in transpiration. = leaf roll.
Phosphorus deficiency or ph issues (preventing phos uptake) can prevent roots from growing at an equal rate of the plant. = leaf roll.
Inadequate or inconsistent watering. =leaf roll.
USDA Zone 7b/ Sunset Zone 31