My system takes a long time to power down if a USB Type-C device, dock, or charger is plugged in or unplugged during the power transition.
A bug in the USB Type-C Connector System Software Interface (UCSI) software implementation in Windows 10, version 1809 can cause a 60 second delay in the system sleep or shutdown process if the power-down happens while the UCSI software is busy handling a new connect or disconnect event on a USB Type-C port. Apart from the extra one minute the sleep or shutdown process takes in this circumstance, this bug does not affect normal functionality of USB Type-C on your machine. The system and the USB Type-C ports should continue to function properly after the next wake or restart of the system.
Edits based on feedback:
1) This is resolved in Windows 10 version 1903, please update to the latest released build if you are impacted by this bug.
2) The issue described only affects Windows 10 version 1809 (17763) and is fixed in 1903.
3) Please use the Feedback Hub for further feedback or questions.