How can we include both Performance ratings and Potential ratings in Performance template?

We are trying to add a section to our Performance Review template for the line manager to provide a Potential rating, and for it to be updated to the employee profile (section visible only to manager).

I am running into the error "The Profile Content section type already exists in the template. A section type can only be used once in a performance template. (HRA-960116) Select a different section type to add another".

In fact there are no Profile Content section types in the document (it seems this section type is in relation to competencies, which we don't use). I assume the error refers to the section where the manager gives their Performance rating, which is updated to the employee profile. This section, and the Potential section I'm trying to add, are set to 'Overall summary' section type.