Im having the same problems and first thought it could be a nutrient def. Then looked for bugs, but I could not find anything.
Suspected that they can be broad mites, since the symptoms was similar to described in Icmag where people thought it was TMV at the beginning and then turned out broad (cylamen) mites. Including Your symtptoms ,I also have twisting in new sprouts.
Link here for the thread in icmag.
I tried avid but it didnt solved my problem.
Lower leafs in shady areas are affected in my case. And also new sprouts. Someting is eating them and I cant frickin find the monster.
My lights will be on in an hour, and Ill post pics.