do you used set and get values to store values ? 

if not 

you should do it like that 

def set_values(self):
    res = super(ResConfigSettingsdurar, self).set_values()
    self.env['ir.config_parameter'].set_param('yourmodelname.partner_id', self.partner_id)
    return res

@api.model
def get_values(self):
 res = super(ResConfigSettingsdurar, self).get_values()
 ICPSudo = self.env['ir.config_parameter'].sudo()
    partner_parameter = ICPSudo.get_param('yourmodelname.partner_id')
 res.update(
        partner_id=partner_parameter,
)
return res

then 
you should get it in yourmodel bu this way 
def get_partner(self):
 partner_from_seeting = self.env['ir.config_parameter'].sudo().get_param('yourmodelname.partner_id') or False
 return partner_form_setting