I had the same problem that my form was always populated with values from the last input.
If the above solutions did not help, here is my solution:
After importing the field group on a new website I unfortunately left the post type ‘page’ under the position rules. So after each saving of the form all form fields were saved in the metas of the page containing the form. These were then prefilled in the form…
After I edited the position rules of the field group and after I deleted the page and put it back up again, everything worked fine again.
Hope this helps someone.
