There is a Section comments added when adding an Additional Comments via manage template.
Reproducing the Issue
Create a new form with "Additional Comments" section. or Add "Additional Comments" Section via Manage template in your form.
As you can see in the image above, Field Permissions is not available for editing or granting to roles.
Permission can be applied in the Form Template's xml in provisioning by support or by a partner.
As a customer, you do not have access to provisioning instance, please contact support.
*For support: See internal memo.
KBA , LOD-SF-PM-FRM , Forms & Templates , Problem