The end of /var/log/dist-upgrade/main.log is showing a unicode decode error:
2016-09-09 14:21:30,594 DEBUG linux-image-4.4.0-9136-generic (new-install) added with 45669149 to boot space
2016-09-09 14:21:31,638 DEBUG dir '/var/cache/apt/archives' needs '180762526' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (21087518720.000000)
2016-09-09 14:21:31,638 DEBUG dir '/usr' needs '354729984' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (20906756194.000000)
2016-09-09 14:21:31,639 DEBUG dir '/usr' needs '52428800' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (20552026210.000000)
2016-09-09 14:21:31,639 DEBUG dir '/boot' needs '91338298' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (20499597410.000000)
2016-09-09 14:21:31,639 DEBUG dir '/tmp' needs '5242880' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (20408259112.000000)
2016-09-09 14:21:31,639 DEBUG dir '/' needs '10485760' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (20403016232.000000)
2016-09-09 14:21:31,640 DEBUG dir '/tmp' needs '0.0' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (20392530472.000000)
2016-09-09 14:21:31,640 DEBUG dir '/usr' needs '0.0' of '<DistUpgrade.DistUpgradeCache.MyCache.checkFreeSpace.<locals>.FreeSpace object at 0x7f94752ca240>' (20392530472.000000)
2016-09-09 14:21:31,643 DEBUG demoted: 'makedev'
2016-09-09 14:21:31,643 DEBUG found components: {'yakkety-security': set(), 'yakkety': {'multiverse', 'universe', 'restricted', 'main'}, 'yakkety-updates': {'multiverse', 'universe', 'restricted', 'main'}
}
2016-09-09 14:21:31,810 DEBUG toinstall: '['btrfs-progs', 'dirmngr', 'gnupg-agent', 'gnupg-l10n', 'libassuan0', 'libicu57', 'libip4tc0', 'libip6tc0', 'libiptc0', 'libjson-c3', 'libksba8', 'libnpth0', 'libpng16-16', 'libprocps6', 'linux-headers-4.4.0-9136', 'linux-headers-4.4.0-9136-generic', 'linux-image-4.4.0-9136-generic', 'linux-image-extra-4.4.0-9136-generic', 'pinentry-curses', 'python3-crypto', 'python3-distro-info', 'python3-httplib2', 'python3-keyring', 'python3-keyrings.alt', 'python3-launchpadlib', 'python3-lazr.restfulclient', 'python3-lazr.uri', 'python3-oauth', 'python3-secretstorage', 'python3-setuptools', 'python3-simplejson', 'python3-wadllib', 'python3-zope.interface']'
2016-09-09 14:21:31,811 DEBUG toupgrade: '['apparmor', 'apport', 'apt', 'apt-transport-https', 'apt-utils', 'base-files', 'base-passwd', 'bash', 'bash-completion', 'bind9-host', 'bsdutils', 'btrfs-tools', 'busybox-initramfs', 'busybox-static', 'byobu', 'bzip2', 'cloud-guest-utils', 'cloud-initramfs-copymods', 'cloud-initramfs-dyn-netconf', 'console-setup', 'console-setup-linux', 'cryptsetup-bin', 'curl', 'dash', 'dbus', 'debconf', 'debconf-i18n', 'debianutils', 'dh-python', 'distro-info-data', 'dmidecode', 'dmsetup', 'dnsmasq-base', 'dnsutils', 'dosfstools', 'dpkg', 'e2fslibs', 'e2fsprogs', 'ed', 'ethtool', 'file', 'findutils', 'friendly-recovery', 'fuse', 'gcc-5-base', 'gcc-6-base', 'geoip-database', 'gettext-base', 'gir1.2-glib-2.0', 'git-man', 'gnupg', 'gpgv', 'grep', 'groff-base', 'grub-common', 'grub-legacy-ec2', 'grub-pc', 'grub-pc-bin', 'grub2-common', 'haveged', 'hdparm', 'hostname', 'ifupdown', 'info', 'init', 'init-system-helpers', 'initramfs-tools', 'initramfs-tools-bin', 'initramfs-tools-core', 'install-info', 'iptables', 'iputils-ping', 'iputils-tracepath', 'isc-dhcp-client', 'isc-dhcp-common', 'iso-codes', 'kbd', 'keyboard-configuration', 'klibc-utils', 'kmod', 'krb5-locales', 'less', 'libaccountsservice0', 'libapparmor-perl', 'libapparmor1', 'libapt-inst2.0', 'libapt-pkg5.0', 'libasprintf0v5', 'libatm1', 'libaudit-common', 'libaudit1', 'libbind9-140', 'libblkid1', 'libbsd0', 'libbz2-1.0', 'libc-bin', 'libc6', 'libcap-ng0', 'libcap2', 'libcap2-bin', 'libcomerr2', 'libcryptsetup4', 'libcurl3-gnutls', 'libdb5.3', 'libdbus-1-3', 'libdebconfclient0', 'libdevmapper-event1.02.1', 'libdevmapper1.02.1', 'libdns-export162', 'libdns162', 'libdrm2', 'libelf1', 'liberror-perl', 'libestr0', 'libexpat1', 'libfdisk1', 'libfreetype6', 'libfuse2', 'libgcc1', 'libgcrypt20', 'libgdbm3', 'libgeoip1', 'libgirepository-1.0-1', 'libglib2.0-0', 'libglib2.0-data', 'libgmp10', 'libgnutls-openssl27', 'libgnutls30', 'libgpg-error0', 'libgpm2', 'libgssapi-krb5-2', 'libhavege1', 'libidn11', 'libisc-export160', 'libisc160', 'libisccc140', 'libisccfg140', 'libk5crypto3', 'libkeyutils1', 'libklibc', 'libkmod2', 'libkrb5-3', 'libkrb5support0', 'libldap-2.4-2', 'liblocale-gettext-perl', 'liblvm2app2.2', 'liblwres141', 'liblzma5', 'libmagic1', 'libmnl0', 'libmount1', 'libmpfr4', 'libncurses5', 'libncursesw5', 'libnewt0.52', 'libnuma1', 'libp11-kit0', 'libpam-systemd', 'libpci3', 'libpcre3', 'libperl5.22', 'libplymouth4', 'libpolkit-agent-1-0', 'libpolkit-backend-1-0', 'libpolkit-gobject-1-0', 'libpython3-stdlib', 'libpython3.5-minimal', 'libpython3.5-stdlib', 'librtmp1', 'libsasl2-2', 'libsasl2-modules', 'libsasl2-modules-db', 'libseccomp2', 'libselinux1', 'libsemanage-common', 'libsemanage1', 'libsepol1', 'libsigsegv2', 'libslang2', 'libsmartcols1', 'libsqlite3-0', 'libss2', 'libssl1.0.0', 'libstdc++6', 'libsystemd0', 'libtasn1-6', 'libtinfo5', 'libudev1', 'libusb-0.1-4', 'libuuid1', 'libx11-6', 'libx11-data', 'libxml2', 'libxtables11', 'linux-firmware', 'linux-generic', 'linux-headers-generic', 'linux-headers-virtual', 'linux-image-generic', 'linux-image-virtual', 'linux-virtual', 'locales', 'login', 'lsb-base', 'lsb-release', 'lshw', 'mime-support', 'mount', 'mtr-tiny', 'multiarch-support', 'nano', 'ncurses-base', 'ncurses-bin', 'ncurses-term', 'net-tools', 'openssh-client', 'openssh-server', 'openssh-sftp-server', 'openssl', 'passwd', 'pciutils', 'perl', 'perl-base', 'perl-modules-5.22', 'plymouth', 'plymouth-theme-ubuntu-text', 'policykit-1', 'pollinate', 'procps', 'python-apt-common', 'python3', 'python3-apport', 'python3-apt', 'python3-cffi-backend', 'python3-cryptography', 'python3-dbus', 'python3-debian', 'python3-distupgrade', 'python3-gdbm', 'python3-gi', 'python3-idna', 'python3-json-pointer', 'python3-jwt', 'python3-minimal', 'python3-newt', 'python3-oauthlib', 'python3-pkg-resources', 'python3-problem-report', 'python3-requests', 'python3-serial', 'python3-software-properties', 'python3-update-manager', 'python3-urllib3', 'python3.5', 'python3.5-minimal', 'resolvconf', 'rsyslog', 'screen', 'sed', 'sgml-base', 'shared-mime-info', 'snap-confine', 'software-properties-common', 'strace', 'sudo', 'systemd', 'systemd-sysv', 'sysvinit-utils', 'tar', 'thermald', 'tmux', 'tzdata', 'ubuntu-core-launcher', 'ubuntu-keyring', 'ubuntu-release-upgrader-core', 'udev', 'ufw', 'uidmap', 'update-manager-core', 'util-linux', 'uuid-runtime', 'vim-common', 'vim-tiny', 'wget', 'whiptail', 'xkb-data', 'xz-utils', 'zlib1g']'
2016-09-09 14:21:31,811 DEBUG toremove: '[]'
2016-09-09 14:23:36,391 DEBUG plugins for condition 'StartUpgrade' are '[]'
2016-09-09 14:23:36,391 DEBUG plugins for condition 'yakketyStartUpgrade' are '[]'
2016-09-09 14:23:36,392 DEBUG plugins for condition 'from_xenialStartUpgrade' are '[]'
2016-09-09 14:23:36,392 DEBUG quirks: running StartUpgrade
2016-09-09 14:23:36,392 DEBUG skipping 'README' (no '.')
2016-09-09 14:23:36,412 DEBUG killing update-notifier
2016-09-09 14:23:36,435 DEBUG killing kblueplugd kbluetooth4
2016-09-09 14:23:36,447 DEBUG killing gnome-screensaver
2016-09-09 14:23:36,459 DEBUG apt btrfs snapshots supported: False
2016-09-09 14:23:36,459 INFO cache.commit()
2016-09-09 14:23:36,459 DEBUG failed to SystemUnLock() (E:Not locked) 
2016-09-09 14:23:36,588 DEBUG doing a pty.fork()
2016-09-09 14:23:36,594 DEBUG pid is: 16386
2016-09-09 14:29:17,100 ERROR got exception '<class 'UnicodeDecodeError'>': 'utf-8' codec can't decode byte 0xe2 in position 0: unexpected end of data 
NoneType
2016-09-09 14:29:17,111 DEBUG confirmRestart() called