After a new revision to Apple this is the reply I've received:
During review, your app failed to launch on iPhone and iPad
running iOS 10.2.1 on Wi-Fi connected to an IPv6 network.
Specifically, when we selected the app on the Home screen, the app displayed a launch image then quit unexpectedly. This may be because iOS 10 uses a watchdog timer for apps; if an app takes too long to complete its initial startup, the operating system terminates the app.
However this is something I've been completely unable to replicate. So it's got me completely confused as, how to approach this issue. Perhaps it is time to join the react-native club...