First try, with an existing bluetooth connection:
Sep 30 14:50:05 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): Activation: starting connection 'OnePlus One Network' (8751240a-aaa3-438e-b1f5-c73b36fc8fa5)
Sep 30 14:50:05 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: disconnected -> prepare (reason 'none') [30 40 0]
Sep 30 14:50:05 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: prepare -> config (reason 'none') [40 50 0]
Sep 30 14:50:05 jak-x230 bluetoothd[869]: bnep%d connected
Sep 30 14:50:05 jak-x230 bluetoothd[869]: bnep0 disconnected
Sep 30 14:50:05 jak-x230 NetworkManager[882]: <info> devices added (path: /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4/3-1.4:1.0/bluetooth/hci0/hci0:12/net/bnep0, iface: bnep0)
Sep 30 14:50:05 jak-x230 NetworkManager[882]: <info> device added (path: /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4/3-1.4:1.0/bluetooth/hci0/hci0:12/net/bnep0, iface: bnep0): no ifupdown configuration found.
Sep 30 14:50:05 jak-x230 NetworkManager[882]: <info> devices removed (path: /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4/3-1.4:1.0/bluetooth/hci0/hci0:12/net/bnep0, iface: bnep0)
Sep 30 14:50:05 jak-x230 ModemManager[877]: <info> (net/bnep0): released by modem /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4
Sep 30 14:50:07 jak-x230 ModemManager[877]: <info> Couldn't find support for device at '/sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4': not supported by any plugin
^[[FSep 30 14:50:35 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: config -> failed (reason 'bluetooth-failed') [50 120 44]
Sep 30 14:50:35 jak-x230 NetworkManager[882]: <warn> (C0:EE:FB:20:05:96): Activation: failed for connection 'OnePlus One Network'
Sep 30 14:50:35 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: failed -> disconnected (reason 'none') [120 30 0]
Sep 30 14:50:35 jak-x230 NetworkManager[882]: <warn> (C0:EE:FB:20:05:96): failed to enable userspace IPv6LL address handling
Without a bluetooth connection, it is worse:
Sep 30 14:52:40 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): Activation: starting connection 'OnePlus One Network' (a21bd89a-8897-4cd2-b7f2-ff25945d6141)
Sep 30 14:52:40 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: disconnected -> prepare (reason 'none') [30 40 0]
Sep 30 14:52:40 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: prepare -> config (reason 'none') [40 50 0]
Sep 30 14:52:41 jak-x230 bluetoothd[869]: bnep%d connected
Sep 30 14:52:41 jak-x230 bluetoothd[869]: bnep0 disconnected
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <warn> (C0:EE:FB:20:05:96): failed to look up interface index
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): Activation: (bluetooth) Stage 2 of 5 (Device Configure) successful. Will connect via PAN.
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: config -> ip-config (reason 'none') [50 70 0]
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <warn> (C0:EE:FB:20:05:96): interface bnep0 not up for IP configuration
Sep 30 14:52:41 jak-x230 NetworkManager[882]: nm_platform_link_get_address: assertion 'ifindex > 0' failed
Sep 30 14:52:41 jak-x230 NetworkManager[882]: client_start: assertion 'ifindex > 0' failed
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: ip-config -> failed (reason 'dhcp-start-failed') [70 120 15]
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <warn> (C0:EE:FB:20:05:96): Activation: failed for connection 'OnePlus One Network'
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <info> (C0:EE:FB:20:05:96): device state change: failed -> disconnected (reason 'none') [120 30 0]
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <info> devices added (path: /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4/3-1.4:1.0/bluetooth/hci0/hci0:12/net/bnep0, iface: bnep0)
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <info> device added (path: /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4/3-1.4:1.0/bluetooth/hci0/hci0:12/net/bnep0, iface: bnep0): no ifupdown configuration found.
Sep 30 14:52:41 jak-x230 ModemManager[877]: <info> (net/bnep0): released by modem /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4
Sep 30 14:52:41 jak-x230 NetworkManager[882]: <info> devices removed (path: /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4/3-1.4:1.0/bluetooth/hci0/hci0:12/net/bnep0, iface: bnep0)
Sep 30 14:52:43 jak-x230 ModemManager[877]: <info> Couldn't find support for device at '/sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.4': not supported by any plugin
It used to work perfectly fine some time ago.