I'm also getting this, but for a Face ID match.
It seems like there's a bug with the simulator that makes it fail with this error every couple of tries.
Here's a video of what I was seeing: https://youtu.be/4GyaOymoHN0
I also filed a radar for this: https://openradar.appspot.com/radar?id=6086985273835520
I got the same error:
Lost connection to coreauthd.
on XCode 9.01 or XCode 9.1 beta.
Same here! Hope they fix this before launch day so we can validate our login flow.
I think it does it on every second FaceID attempt. I can repeat it consistently. It looks like it's been fixed in the full Xcode 9.1 release. Testing with a simple local auth attempt works consistently now.