I Have four plants, two are just great, they flower the leaves are growing the way they should and they are all in an east window on a table. The other two are totally different. One is flowering some but the leaves are so small. The other plant has been re-potted and now the leaves are bunched in the middle and growing upward. They sit in a filtered light early and later in the day the light changes and they are somewhat in a darker light although they sit under a lamp in the evening as well. I water from the bottom with room temperature water and feed often.
Sounds like you know how to take care of your violets. I will say something about the lamp you use in the evening. It doesn't help your plants at all. Sorry, but its true. Only a fluorescent light has the spectrum to adequately promote growth and lighting in violets. It is the only type of light that is good to use instead of true sunlight. It has to do with SPECTRUM and foot candles, something I know very little about, but I do know this. If they are getting proper filtered sunlight they don't need lamps at all.
As for the two that are not doing too well, my theory is that you probably shouldn't have repotted them. African violets are plants whose roots NEED to be crowded in order to bloom. You can top dress them once or twice a year, by adding fresh soil to the top and mixing it in, but to repot them into larger pots encourages the roots to grow, which seems positive; however, when the roots grow more the flower doesn't bloom as much. I just learned of this about five years ago myself. Violets are different from other houseplants in so many ways! But that's why we love them.
So, unless the violets are in excessively large pots, don't repot again; just keep them moist, high humidity and good eastern sunlight. It may take a few months, but they should recover.