The app works in Debug and Release mode when launched from XCode 10 beta 6 and earlier onto iOS 12 beta 9 and earlier.
The app crashes on startup (only when downloaded from Testflight) after showing the launch screen for a second or two.
The app works on iOS 11 and iOS 10 when installed via Testflight as well as XCode.
I thought newer releases of the betas may fix the problem but the problem has persisted through each XCode 10 beta, iOS 12 beta, and macOS Mojave beta update.
I added logs that write to a file locally on the device, these logs show that I am not getting past the initial webview.
There are no crash logs from testflight in Organizer for the build.