After submitting a form on a landing page, the Thank-you page fails to load, or it loads the wrong page.
The Thank-you page used by the form can be defined in two places, at the Form level
and at the Landing Page level.
If these two are in conflict, the setting on the Landing Page wins. To troubleshoot this issue, compare the two Thank-you options and make sure the Landing Page is either set to the correct page, or that it allows the Thank-you to be form-defined.