UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10032.21.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.26 Safari/537.36
Platform: 10032.21.0 (Official Build) beta-channel cyan

Steps to reproduce the problem:
1. Shutdown or reboot Chrome OS.
2. Shutdown process starts and screen goes black but never reboots or shuts down.
3. Eventually, a hard reboot - pressing the power button for 5-10 seconds - is required to restart Chrome OS.

What is the expected behavior?
Chrome should shutdown or reboot as expected.

What went wrong?
I don't know if crash reports capture what's going on during a shutdown but, if so, I uploaded two of them that might point to the source of this bug.
1fd2170575b568c0
bfe0061f785593e2

Did this work before? N/A 

Chrome version: 63.0.3239.26  Channel: beta
OS Version: 10032.21.0
Flash Version: 27.0.0.180