ACF 4 and ACF 5 work completely differently. ACF 4 had the post type ‘acf’. ACF 5 has replace this with 2 post types ‘acf-field’ and ‘acf-field-group’. It is not possible to use XML to export field groups from a site using ACF 4 and import those groups into a site using ACF 5.
There is only one way I know of to resolve this. That would be to upgrade the site using ACF 4 to ACF 5 before doing the export.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users