I think your problem is one of continuing moisture, possibly with low temperature thrown in (just a guess).

In nature, tolumnias live on tiny twig branches of shrubs on the windward side of Caribbean islands. They get frequent, drenching rains, but are continually swept with warm, tropical ocean breezes, so don't stay wet for very long.

I have often had issues when trying them with any growing medium, but they do well for me growing on bare cedar slabs or in tiny clay "thumb pots" (about big enough to fit your thumb into) with no medium at all.

About the only exception is a plant I have now, planted in wood fiber in a plastic net pot, but it looks like all the roots in the fiber have rotted, so the plant has resorted to growing on the outside, instead.