On closing sessions under su I got the error “xxx: No module specific data is present”. With the help of the Debian bug report #73664 I tracked this down to libpam-ssh and it turned out, the error message went away when I created a (dummy) ssh key by ssh-keygen for the user inquestion (i.e. the user who's session did end).

Please note the error message might not show up connected to libpam-ssh but to any module listed afterwards in /etc/pam.d/common-session or process invocing the session as cron or su.