I just installed 4.8.0-34 via apt-get dist-upgrade and can no longer login to the desktop. I can, however, ssh in, and I see these messages in /var/log/auth.log:

Jan 10 23:10:12 scruffy lightdm: pam_unix(lightdm-greeter:session): session closed for user lightdm
Jan 10 23:10:12 scruffy lightdm: pam_unix(lightdm:session): session opened for user waltman by (uid=0)
Jan 10 23:10:12 scruffy systemd-logind[1419]: New session c12 of user waltman.
Jan 10 23:10:12 scruffy systemd-logind[1419]: Removed session c11.
Jan 10 23:10:19 scruffy lightdm: pam_unix(lightdm:session): session closed for user waltman
Jan 10 23:10:20 scruffy lightdm: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
Jan 10 23:10:20 scruffy lightdm: PAM adding faulty module: pam_kwallet.so
Jan 10 23:10:20 scruffy lightdm: PAM unable to dlopen(pam_kwallet5.so): /lib/security/pam_kwallet5.so: cannot open shared object file: No such file or directory
Jan 10 23:10:20 scruffy lightdm: PAM adding faulty module: pam_kwallet5.so
Jan 10 23:10:20 scruffy lightdm: pam_unix(lightdm-greeter:session): session opened for user lightdm by (uid=0)
Jan 10 23:10:20 scruffy systemd-logind[1419]: New session c13 of user lightdm.
Jan 10 23:10:20 scruffy lightdm: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
Jan 10 23:10:20 scruffy lightdm: PAM adding faulty module: pam_kwallet.so
Jan 10 23:10:20 scruffy lightdm: PAM unable to dlopen(pam_kwallet5.so): /lib/security/pam_kwallet5.so: cannot open shared object file: No such file or directory
Jan 10 23:10:20 scruffy lightdm: PAM adding faulty module: pam_kwallet5.so
Jan 10 23:10:20 scruffy lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "waltman"