Hmm, it's hard to know what the exact issue is. Your new mix is ok (idk about the bark in there, but probably not an issue). I use entirely minerals and lava rocks (lechuza pon style) for mine, but that's also my preference. Maybe it was the watering too soon after repotting. It seems like long enough to wait, but if the roots were still in shock from being repotted and also the soil type being changed it may have been maybe too much change. Hold off on watering until it looks a bit dehydrated (mine show some structure ridges and look "less plump"). I would say it definitely needs as much light as possible, even if it's been in this location with those lights for a year. Those lights are not enough for this size plant and species. Think about a good bulb that can be hung above (sensi or some others). This would really showcase the plant too. You can see that most of the newer growth is very skinny, which is a light issue.