Most likely the rot is from over watering. Your mix looks too fine for Catts, IMHO.

Depending on the Catt...some won't develope new roots until new growth is initiated, others won't until quite some time after a new growth matures and flowers. I try to not repot until I see new roots starting to grow. I use a well draining medium and allow it to dry between waterings.

I don't have one consistent medium I use for Catts. Some I have mounted on cork, like C. walkeriana. One I have in a basket of LECA (S/H medium). Some are in S/H, many in medium bark mix. I have one that I am trying mounted on Epiweb. I have one in course diatomite.