It is a user issue. This usually happens when someone uses a program other than Adobe Reader or Acrobat to fill in the form, such as Mac Preview. You can simply put a text box on the form prompting the user to download and fill in using Adobe Reader with a link to the website OR if you do recieve a form this way you can "re show" the fields by following these steps. (Assuming you have at least Adobe Acrobat Standard):
Open form with hidden data.
Go to Forms>Manage Form Data>Export Data
Save the file as XDP. Close the form.
Reopen and go to:
Forms>Manage Form Data>Import Data
--import the XDP file you just created.
All your fields should now be showing. Saves time when you have an extensive form. Keep in mind some of your data may not have auto formatting since the user did not use Adobe to fill in the form and some fields may require "cleaning up."
Brenda