Looks to me like a PH problem caused by too much nutrients building up in the soil. This creates hot spots. Too much of a fluctuation.
It may be possible that some nutrients have been locked out. I thought I could see some other plants leaves curling inwards too.

Also, what is your humidity ? Is it very dry in there ?

Anyway, I would back off with the nutrients and give the plant a very good flush with distilled water if you have it. How accurate is your PH reading ?
Take another PH reading, correct it and see how it behaves over the next week.

good luck with it.