I solved the issue above by editing the handler that is responsible for rewriting the permalinks in relation to WPML.
This is done by editing the file ‘translate-rewrite-slugs.php’ located in the ‘/includes/libraries/’ subdirectory of the plugin-folder.
On line 263 I added the missing slash after the home_url which results in the following edited line:
$post_link = esc_url( icl_get_home_url() . '/' . $this->post_types[$post->post_type]->translated_slugs[$lang]->rewrite['slug'] . '/' . ( $leavename ? "%$post->post_type%" : $post->post_name ) );
After this you have to re-save the permalinks in the plugin settings (most right tab), followed by flushing your site permalinks.