F11, F12 don't change volume.

When I press F11 or F12 to try to change the volume, rather than the small segmented bar on the bottom, I get the "international not symbol". The volume doesn't change, either. I can mute with F10, and I can change the volume in system preferences.

This is A1502 MacBook Pro; I just upgraded to Sierra (yes, rather late) and this is new behavior since the upgrade.

Thanks.