Mate, does funkcion wp_mkdir_p has something in common with open_basedir?
Becouse have such a error:
PHP Warning: is_dir(): open_basedir restriction in effect. File(/) is not within the allowed path(s): (/home/admin/:/tmp/:/var/tmp/:/usr/local/php56/lib/:/usr/local/php54/lib/:/usr/local/php55/lib/:/usr/local/php56/lib/:/usr/local/php70/lib/:/usr/local/php71/lib/:/usr/local/lib/php/) in /home/admin/domains/alitopbrand.pl/public_html/wp-includes/functions.php on line 1613\nPHP message: PHP