Not sure if I understand your problem and solution, but I’m having a problem where my Gravity Form is saving to the Posts post type instead of the custom post type, which I can indeed see in the Advanced tab on the field and can indeed set to the correct custom post type. The entry is just not going to the right place.
It sounds like you’re setting the post type after submission, so I wonder will this help me force it into the correct post type? What do you think?
And where are you enter this add_action exactly? What file and what plugin? Thanks!