Tolumnia leaves falling off
 

I have 3 tolumnias mounted and one has started loosing its leaves when you touch it what could be wrong the leaves are still green.

From what you describe I would suspect either rot or insufficient water. Mounted Tolum's should have relatively high humidity with good air movement. What is it mounted on?

Also check it for scale. Scale loves to hide down in those folded leaves.

Learn about Tolumnia here:
Darryl Venables on Tolumnia - DVOS September 2018

mounted on a piece of cork