Im not sure the EXACT cause, but when it happens to me, I feel its a relationship between what would normally be normal nutes becoming too much from leafs getting closer to the light and having to transpire more water than it needs to absorb nutrients, so I think the leaf twists to avoid getting too much light forcing them to transpire too much. Try raising the light, or flushing and reducing nutrients... And more mag which will help with energy....i think. But dont take it as gospel....