Just out of curiosity, why did you choose to run such an old distribution (16.04) of Ubuntu on a relatively new laptop?

I just happened to receive a marketing email from Lenovo this morning (I've bought a few PCs from them in the past) that included the Carbon X1 Gen 7 and I looked it up.  It has USB 3.1 ports (2x Gen 2 Type-C with Thunderbolt and 2x Gen 1).  I'd think that you'd need the latest possible version of Ubuntu (and the Linux kernel) to support this laptop. 

Looking at the Ubuntu certification page for the Carbon X1, it shows as having been tested with Ubuntu 18.04 LTS 64-bit.

Your symptoms (device appears, disappears, works sometimes but not others) could be due to instability in the underlying kernel support for the motherboard and/or USB controllers.

Another issue to investigate is the use of USB 3.1 ports.  In the past there have been issues with USB 3 ports causing RF interference with devices that are connected.  This mostly manifests with wireless keyboards and mice, but it wouldn't surprise me if it was an issue here.  The common fix is to use a USB extension cable to move the USB device away from the port.

I had connected the cable, tried to access it from chirpw causing it to disconnect a few times, by the time I did dmesg. I removed out the multiple connect/disconnect lines from dmesg output because the information was mostly duplicate.

On Mon, Feb 17, 2020 at 7:24 PM Tom Henderson <Tom@henderson4.us> wrote:

Just double checking here. The log messages below show the cable connecting, and then disconnecting. Had you disconnected the cable again before running dmesg, or did the cable fail?

Tom Henderson

On 2/16/20 11:56 PM, Kheong Sann CHAN wrote:

The tty port is found when I plug it in:

$ dmesg | grep tty
[ 7527.188154] usb 1-2: pl2303 converter now attached to ttyUSB0
[ 7548.490452] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0

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