I am experiencing intermittent crashes when I ran my iOS app in the simulator in the below environment MacOS 10.13.6
Xcode Version 10.1 (10B61)
Simulator iphone xs iOS 12.1
Swift version 4
Here is the error I get.
Assertion failed: (fState == kTubeStatePostConnectConfiguration), function _onqueue_resetAndReconnect, file /BuildRoot/Library/Caches/com.apple.xbs/Sources/CFNetwork_Sim/CFNetwork-975.0.3/Connection/Establishment/Tube.cpp, line 514.
I have seen this error intermittently with other simulators as well. Not sure how to debug these kind of errors where it crashes the app on a random thread with out knowing line causing crash.
A stack trace is shown if you click on the text all the way to the right of the debugger buttons. You should be be able to see the last method called before the error occurred.
I had a similar crash, deleting the app from the simulator followed by a clean compile fixed it.