Update line 109 for fixed wrong import categories:
Old code: //$categories[$cat_index] = $wpdb->escape( html_entity_decode( $category ) );
New code: $categories[$cat_index] = str_replace(array(‘<![CDATA[‘, ‘]]>’), ”, $wpdb->escape( trim($category) ));

PHP Fatal error: Uncaught Error: Call to undefined function set_magic_quotes_runtime() in /var/www/wordpress/wp-content/plugins/rss-importer/rss-importer.php:72\nStack trace:\n#0 /var/www/wordpress/wp-content/plugins/rss-importer/rss-importer.php(178): RSS_Import->get_posts()\n#1 /var/www/wordpress/wp-content/plugins/rss-importer/rss-importer.php(204): RSS_Import->import()\n#2 /var/www/wordpress/wp-admin/admin.php(308): RSS_Import->dispatch()\n#3 {main}\n thrown in /var/www/wordpress/wp-content/plugins/rss-importer/rss-importer.php on line 72, referer: https://marvin.fablab.fau.de/wp-admin/admin.php?import=rss

Causes errors with current versions of both PHP and WordPress