I have experienced two problems for USB tethering on Lubuntu 18.04:
I tried USB tethering from Android 4.4.4 Samsung Galaxy Grand smartphone to Lubuntu 18.04 32-bit desktop computer, but the Android device asks me the PIN code for my SIM card a few seconds after connecting the USB cable. And then the Android device chills, though I enter the PIN code. And I have to disconnect the USB cable and reboot the Android device.
I tried USB tethering from an Android 5.1.1 Everest tablet to Lubuntu 18.04 64-bit desktop computer. As soon as connecting, the tablet suddenly restarts. And so I failed tethering, again.
Is there any way to cope with these vexing problems?