Symptoms

If you enable hidden checkbox for existing workflow process data fields, it causes previous data mappings on the Start Workflow action to be removed when editing the action and you get the warning message below:

"The configuration has been adjusted automatically. Mappings were found that are no longer valid for the context. These mappings have been removed.
Save these changes or they will be lost."
 

Diagnoses

This is currently as designed.
 

Resolution

One way one can get around this is to un-hide the hidden process data fields.

A feature request has been logged for the ability to hide data in workflow reporting without breaking workflow design. This is intended to cater for scenarios where the data NEEDS to be hidden due to its sensitive nature or if it's highly protected information.