Let me see if I am understanding the situation correctly. You have had two for some time, these have been re-potted this summer and are not doing well. A third is fine and not at issue. Of the two that were re-potted you used the same prepared bonsai mix for both. These are the ones potted in the brown oval pot and the purple plastic one. Is all this correct?
The soil in the ceramic pot looks pretty good from here but you are in a better position to judge it than we are. The soil in the plastic pot looks a little different, but again that may not really be the case.
As I mentioned I am not familiar with this species and I am not encouraging yo to re-pot but if you do I feel I should mention a few things. Bonsai soils are generally soilless but not necessarily 100% inorganic. Most plants will do well in a mix that includes some organic material, this does not mean soil but is usually bark in pieces similar in size to the balance of your mix.
Harry Harrington (Bonsai4me) suggests a basic mix which, to me, implies that bark is included. Not sure how much, one third seems like a place to start. Remember, bonsai soil is all about consistent size, removing the fines and providing excellent drainage.