If you are facing a situation that your app crashes only on TestFlight build then you need to follow following steps
- Add you apple account to your Xcode. You can do this by going to Xcode-> preferences->Accounts. Click on the + button and the same apple developer account which you are using for test flight.
- Simulate crash on a device. You need to install the build from TestFlight and re simulate the crash. You will b4e prompted to send crash report to developer. send it.
- No back to your Xcode. Go to Go to Xcode->widows->organiser then select crashes tab then select your app. Here you will see the crash and specific issue causing it.
I have noticed that in case of old apps which are updated recently this issue is mainly due to UISearchDisplayController you need to replace it.