Saya baru saja mengalami masalah yang sama persis setelah memutakhirkan ke 16.04.1 dari 14.04 (di mana penambatan USB berfungsi dengan baik selama bertahun-tahun).
Berdasarkan syslog sepertinya disebabkan oleh konflik dengan ModemManager.
Aug 25 13:12:24 outback NetworkManager[2543]: <info> [1472145144.1334] device (enp0s20u2): Activation: successful, device activated.
[...eliding log entries related to nm-dispatcher services]
Aug 25 13:12:38 outback ModemManager[2503]: <info> Creating modem with plugin 'Generic' and '2' ports
Aug 25 13:12:38 outback ModemManager[2503]: <info> Modem for device at '/sys/devices/pci0000:00/0000:00:14.0/usb3/3-2' successfully created
Aug 25 13:12:41 outback ModemManager[2503]: <warn> couldn't load Manufacturer: 'Serial command timed out'
Aug 25 13:12:44 outback ModemManager[2503]: <warn> couldn't load Model: 'Serial command timed out'
Aug 25 13:12:47 outback ModemManager[2503]: <warn> couldn't load Revision: 'Serial command timed out'
Aug 25 13:12:50 outback ModemManager[2503]: <warn> couldn't load Equipment Identifier: 'Serial command timed out'
Aug 25 13:12:50 outback ModemManager[2503]: <warn> couldn't load Operator name: 'SIM failed to handle CRSM request (sw1 106 sw2 130)'
Aug 25 13:12:54 outback ModemManager[2503]: <warn> couldn't load IMEI: 'Serial command timed out'
Aug 25 13:12:54 outback ModemManager[2503]: <info> Modem: state changed (unknown -> disabled)
Aug 25 13:12:54 outback NetworkManager[2543]: <info> [1472145174.3879] device (enp0s20u2): state change: activated -> deactivating (reason 'connection-removed') [100 110 38]
Aug 25 13:12:54 outback NetworkManager[2543]: <info> [1472145174.3881] manager: NetworkManager state is now DISCONNECTING
Aug 25 13:12:54 outback NetworkManager[2543]: <info> [1472145174.4362] dns-mgr: Writing DNS information to /sbin/resolvconf
Aug 25 13:12:54 outback dnsmasq[4348]: setting upstream servers from DBus
Aug 25 13:12:54 outback NetworkManager[2543]: <info> [1472145174.4430] manager: (ttyACM0): new Broadband device (/org/freedesktop/NetworkManager/Devices/4)
Aug 25 13:12:54 outback NetworkManager[2543]: <info> [1472145174.4441] device (ttyACM0): state change: unmanaged -> unavailable (reason 'managed') [10 20 2]
Aug 25 13:12:54 outback NetworkManager[2543]: <info> [1472145174.4445] device (ttyACM0): modem state 'enabling'
Aug 25 13:12:54 outback NetworkManager[2543]: <info> [1472145174.4457] device (enp0s20u2): state change: deactivating -> disconnected (reason 'connection-removed') [110 30 38]
Saya menonaktifkan ModemManager melalui perintah:
sudo systemctl disable ModemManager.service
Dan kemudian reboot. Sesi tethering USB saya berikutnya telah stabil sejak saat itu.
Saya yakin ada cara untuk mengkonfigurasi ModemManager dengan benar untuk ponsel saya (LG G3), tetapi saya tidak memerlukan modem serial saat ini, jadi metode ini berfungsi untuk saya.