Hmmm, I thought that would be it for sure. Have you been monitoring the pH of the water you give them? Did you give them any ferts or other additives in the water recently? Ferts added to the water will cause the pH to plummet, and a fluctuating pH can cause plants to do wierd things. If you aren't measuring and adjusting the pH, then it would be very different depending on if you add ferts/other additives or not.
You should also take a pH reading of your runoff from the drainholes in your pot, to see if your soil is getting too acidic or too alkaline. If it is too low or high, do a flush on the plants to help restore the soil pH to the correct level ( 6.5-6.8 ).
There are also viruses that can infect your plant and cause the leaves to do strange things. Check out this thread on
Tobacco Mosaic Virus and other viruses that affect a large % of cannabis plants these days because most people do not realize it is a virus and attribute damage to something else, like over or under fertilizing.