IOS UI SDK fails to load on only one particular device

We are launching an ios app. The app is currently in testflight for testing purposes. The app works on other devices using my credentials but just fails to load on my device. We have not been successful yet to figure what the issue is. Please help or share some insights into if you have seen something like this before.

You should tell you use Firebase.

And show the full code of ViewController.swift which seems to be the cause of crash. Even though the line number is surprising.

IOS UI SDK fails to load on only one particular device
 
 
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