gistfile1.txt

        /* Gravity forms merge tags on multi page form

        There seems to be a bug in Gravity Forms, when you're using custom Merge Tags; 
        normally, an empty input value will be replaced by the
        "default value", if you use the Default Value option in Gravity Forms.
        On multipage forms this means that fields that were left empty _intentionally_ on page one will
        be overwritten by the default value as soon as you load page two (and so on).
        
        This is a fix I came up with.
        Replace "CustomMergeTagName" with (part of) your custom Merge Tag, or leave those lines out entirely
        if you want to apply this fix to ALL (default and custom) Merge Tags.
        */

        add_filter( 'gform_field_content', function ( $field_content, $field, $value, $entry_id, $form_id ) {
            $current_page = isset( GFFormDisplay::$submission[$form_id] ) ? GFFormDisplay::$submission[$form_id]['page_number'] : 1;
            if( rgar( $field, 'pageNumber' ) != $current_page ) {
                if (isset($field['inputs']) && is_array($field['inputs'])) {
                    foreach ($field['inputs'] as $input) {
                        $postName = 'input_' . $input['id'];
                        if (
                            isset($input['defaultValue']) &&
                            strpos($input['defaultValue'], 'CustomMergeTagName') !== false &&
                            isset($_POST[$postName]) &&
                            $_POST[$postName] == ''
                        ) {
                            $val = esc_html($value);
                            $field_content = preg_replace('/ value=\'' . $val . '\' /',' value=\'\' ',$field_content);
                        }
                    }
                }

                $postName = 'input_' . $field['id'];
                if (
                            isset($field['defaultValue']) &&
                            strpos($input['defaultValue'], 'CustomMergeTagName') !== false &&
                            isset($_POST[$postName]) &&
                            $_POST[$postName] == ''
                ) {
                    $val = esc_html($value);
                    $field_content = preg_replace('/ value=\'' . $val . '\' /',' value=\'\' ',$field_content);
                }
            }

            return $field_content;
        }, 10, 5);