Error while fetching child table value on webform for guest

We are creating an child table in a doctype and for same doctype we create an webfrom now on web form the error was coming for guest for loged in user it’s working fine

the error was “Not Permitted” Permission error coming on webform when we click on add row in child table on webform.

Same Bug in V13 & V14

Is there any solution for this. (1)