USB to Serial Adaptor works once for every reboot...

I have a USB to Serial Adaptor for connecting to CONSOLE port of switch/router and I use "screen" inside Terminal to connect. Recently I found the "screen /dev/cu.usbserial 9600" works only once for every system reboot. Here are the steps to replicate:

1. The output of "ls /dev/*usb*" shows the correct device.

2. Login to console of the device with "screen /dev/cu.usbserial 9600"

3. Press "Ctrl+A, Ctrl+K" to exit screen

4. (optional), disconnect/reconnect the usb to serial adaptor from laptop OR disconnect/reconnect the console cable from target device.

5. The output of "ls /dev/*usb*" still shows the correct device.

6. Try to connect to console again with "screen /dev/cu.usbserial 9600", the screen process will hang. Once that is happening, the screen process can not be killed via "sudo kill -9" and only be solved by complete power cycle. BTW, the laptop will also hang during reboot/shutdown, until I keep pressing on power button...

7. Once screen hang, The output of "ls /dev/*usb*" would show nothing.

Once laptop boots up again, I can connect with the same screen command and same scenario for step 2-3 above...

I have Mac OS 10.11.3 and adaptor is Micro Innovations branded (Prolific chip). I downloaded and installed/re-installed driver from Prolific site and no difference...

Any idea?