After updating X1 to 3.0.5.0, I was invited to update the firmware on my Z1.  Unfortunately, the firmware update just sat there fore over 10 minutes (and the mouse still worked) so I killed the X1 control panel and restarted it.  This condition persisted through at least 2 more reboots.

Eventually I unplugged and replugged the mouse, and the firmware update successfully ran.  FYI to anyone having the same issue.