Hello Jiri,I have faced the same problem. I think there is something wrong with the sssd-nss socket unit /lib/systemd/system/sssd-nss.socket
After I disabled it by # systemctl disable sssd-nss.socketthe problem has disappeared and my system (Stretch) boots normally. SSSD works. NSS through SSSD (LDAP) works too, the domain users and groups are visible. The socket is created at /var/lib/sss/pipes/nss.
-- Alexander Lebedev <meved...@yandex.ru>