Just a bug. Will get sorted out. I had the same issue. Then today all of sudden it was back. I think I went to settings and turned off Nav on AP, then turned it back on. Or vice versa. Not sure if that had anything to do with it, but the button was back today and I didn't have an update on the car since yesterday.
Just be patient. Remember, any time you have an issue, try rebooting before you do anything. That solves 90% of the issues.