So thanks to this thread - https://developer.apple.com/forums/thread/124265, I finally found an answer. See Quinn's response below :
iOS 13 introduces new behaviour (r. 47718087) whereby, if the user has turned Background App Refresh off in Settings — either globally or for your app, assuming it has this setting — your app won’t be resumed (or relaunched) when the tasks complete in an NSURLSession background session. That is, your session will behave as if sessionSendsLaunchEvents were set to false.
Topic:
Programming Languages
SubTopic:
Swift
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