Problem with WorkFlow and field DueDate

Hi Friends,

I have a big problem with a WorkFlow created in my site of Sharepoint 2013 Online:

The workflow task list has lost the filed called "DueDate" and now the workflow crashes after create a task in the task list. 

The error is the following: The filed or property 'DueDate' doesn't exists

I have tried to add the field to list across type content "Task", type content "WorkFlow Task" or directly across site column called "Due Date", but in both cases, adds a column named "TaskDueDate" against "DueDate".

However, if I create a new task list, automatically includes the field "DueDate", but I can't find the way of add this field to a existing tasks list.

If I find that column in "site colums" typing the URL manually, It´s show but in a group called "_Hidden" but I don't find the way of adding that column to a existing content type or list.

Thank you!!