I'm getting the same apparent crash as dyld`__abort_with_payload: With no error message but only on the Apple Watch.
I suspect it's related to CocoaPods, since this watch app uses Pods, and my other watch app (which does not have this issue) does not. Another clue is that this is not a problem when deploying to watchOS 6 or from Xcode 10.
It's a long shot, but has anyone else got some insight?
Update: Interesting finding... Removing the pod 'Mixpanel' from the watch extension fixed the crash...
Update 2: Using 'Mixpanel-swift' in the watch extension causes this same issue.