Please refer to the upgrade instructions corresponding to your installation method.
get_cookie() when $xssClean is true changed the output. Now it uses FILTER_SANITIZE_FULL_SPECIAL_CHARS, not FILTER_SANITIZE_STRING. Make sure the change is acceptable or not. Note that using XSS filtering is a bad practice. It does not prevent XSS attacks perfectly. Using esc() with the correct $context in the views is recommended.