I developed an iOS app along with the Watch OS app.
We are using an iPhone camera for capturing video.
To capture video iPhone app needs permission from the app user.
When iPhone displays a permission dialog and the user allows/disallows permission respective Watch App gets killed with debugger signal 9.
If I remove camera permission then the Watch app works fine.
Also, Not only camera permission If the user at some point changes the Address Book, Calendars, Reminders, Camera, or Photos permissions, WatchOS app will SIGKILL the app when change App permission in iPhone. (it's default behaviour of iOS and WatchOS)
Please refer the below links
App killed by SIGKILL when changing privacy settings , https://developer.apple.com/forums/thread/64740, App crashes in background while changing permission - swift, App crashed in iOS 6 when user changes Contacts access permissions