I also have other plants of the same age, in 2 liter pots, which are still in the greenhouse and have received the same treatment but show no symptoms... only the plants that have been transplanted have this problem. I used the same soil for the transplant. I'm speculating it's not an abiotic problem, nutrient or soil... but biotic... although I haven't seen any signs of parasites.
You are asking people who use an EC or TDS meters. IF you got yourself one, you would know the answer to your own question better than them. Get yourself an EC meter because they are so easy to use and so much fun. It's the difference between someone that knows what they are doing and ones that don't.