Why is the Sorting function in the Priority Table Disabled?
The Sorting function for the Start Date, End Date, and Progress columns in the Priority table is disabled when the board contains projects with different settings for the Field Mapping(of the same fields)—some with it enabled and others with it disabled.

For example:
When a user creates a Roadmap board with two projects (Project A and Project B):
Project A has the Project Field Mapping feature enabled
Project B has the Project Field Mapping feature disabled

The Sorting of these columns in the Priority table will also be disabled if the board contains projects mapped with different fields for each project.
Example:
Sorting on the Start date column in the Priority table will be disabled if:
Project A has the Start Date and End Date mapped with Start time 1 and Due time 1 fields
Project B has the Start Date and End Date mapped with Start time 2 and Due time 1 fields

