Authproc filter ignored when logging into php application

i have set up a global authproc filter in my config.php of my simplesamlphp to have 2fa.

it works fine for all sp applications. (wordpress, moodle,…)
however i do have a self made php application, which does the following to login in

$as = new \SimpleSAML\Auth\Simple(‘default-sp’);

the login (first factor) still works, however the 2nd factor, which should be handled by privacyidea, is never triggered.

any idea?