Can't access "Ok Google" Screen

[Android Central Question]

I've got a Nexus 6P running 8.1.0

I go to the Google app, and tap the menu icon in the upper-left, then tap Settings.

I tap Voice.

Then I tap "Ok Google" detection.

Another screen--I'm assuming it's the "Ok Google" detection screen--flashes on for about half a second. Then I'm back at Voice. I can't change any Ok Google settings.

Anyone have a suggestion?