Personally I'm not surprised if their not getting enough light. The light intensity drops dramatically the farther away from the foliage florescent
lights are in comparison to HID lighting. Now that the tomato plants are taller than a foot or so, the lower leaves aren't getting nearly as much light as they used to when the plants were shorter (and the lights were closer to them). So the lower leaves just aren't getting enough light for photosynthesis anymore. And photosynthesis is even more important to the plant when it's fruiting.