There’s a bug in Gravity Forms causing data to not be included in personal data exports and personal data removal requests. It affects sites relying on User ID as identifier for form submissions. The bug was introduced in a Gravity Forms version between 2.4.21 and 2.5.15. The support team denied me access to their versions archive, so I don’t know the exact version.
In the class GF_Personal_Data, a string (“created_by”) is run through the absint() function, causing 0 to get saved to the database instead of the string. A quick workaround for this is to simply removed the call to absint(), see class-personal-data.php line 520. Since incorrect data has been saved to the database, you must re-save all affected forms after the change.
(I reported this to the developers a month ago and I’ve sent a reminder as well. Unfortunately, they haven’t responded or fixed the issue in neither of the two updates released since then.)