I hope I'm not overdoing this response, but...

OF COURSE you get root rot when transferring a plant into S/H culture. It is expected.

When roots grow, they "tailor" themselves on a cellular level so that they will function optimally in that environment, and once those cells have grown, they cannot change. Move them into a different environment, and those roots are no longer optimal for the environment, so are stressed, and will eventually die and rot. How quickly that happens is determined by the degree of difference between old and new root zone environments.

Even old bark and fresh bark constitute different environments. (I'll create another thread on that in a moment)

That is why it is important to repot just as new roots are emerging from the plant and actively growing. They will be tailored for the environment and support the plant, while the old roots fade away.