Laptop fails to fully shut down after using USB devices

User Support Hardware Issues
1

I am using a Lenovo Yoga C940, and seeing weird shutdown behavior which I did not observe on my previous Linux installation (Manjaro).

When I shut down the computer via the xfce menu, one of three things happen:

  1. If I have forwarded USB keyboard/mouse from sys-usb, right after the message about successfully unmounting /oldroot it then enters a state where the screen backlight, power status light, and fan remain on and the keyboard backlight still activates, but nothing is visible onscreen. I have activated the systemd debug shell following this shutdown troubleshooting guide, but the debug shell is inaccessible once my laptop enters this state. I have several times left it in this state for 10-20 minutes, with no change. This also rarely occurs even if I have not forwarded a keyboard or mouse.
  2. Otherwise, if the laptop is running on battery, it reboots.
  3. Otherwise (if the laptop is on AC power), it shuts down successfully.

I have sometimes seen exceptions to these rules, but not frequently.

Any advice on how to diagnose?