As it looks like it is only affecting the new tender growth, I would suspect the sun is doing the damage. Perhaps you could provide morning sun/afternoon shade to see if that will provide some relief.
In the south, I find these large leaf basils are more prone to this type of damage.
You can also remove the damaged foliage if you wish. The pruning won't hurt it at all.
And I'll watch this thread. If I'm wrong, I'll learn from it.

Good luck!