Best practice to avoid issues such as blank tags even when having access to the field. We compile DocGen Packages to efficiently make calls out to Salesforce.
Any time the metadata or a document changes, we gather all the information we can pull from Salesforce for subsequent runs. If the user that initially runs the package after the change does not have access to the field, we do not include the field in the compiled information.
Best practice: make sure that the admin who has access to all fields to run the package after the changes are made as well as ensuring the users that are running the package has access to the fields used in the document package.