I have had the same issue with some of my plants, and I think it is pH related. Do you actively check the pH of your water+nutrients AND your runoff? If you can test the soil directly that is ideal, but you should know exactly what the pH is of everything that goes in and comes out of your plants. Some plants are also more sensitive to pH imbalance than others, which is why only one plant might be showing signs of "the claw" as I like to call it. Dropping it and repotting certainly could stress it, but I don't think it would stress it into curling under like that.