Something seems broken: the journal is filled up with such messages (PAM unable to dlopen(pam_winbind.so): /lib/security/pam_winbind.so...) and ldap auth seems no longer working for my everything-up-to-date installation 5.0.7/xenial.
So, please, who has a still working installation? Please report the samba packages installed for you. Perhaps I get it up and running again by downgrading ...