TestFlight reports crash when app running in background

Hi, I have an app distributed to TestFlight beta testers. They reported from time to time when the app running in the background by launching another app for a while, suddenly TestFlight crash report dialog comes up, this happens most often on iPhone.

I don't have any tasks processing/running in the background from my app.

So I'm wondering TestFlight reports this kind of crash due to iOS removing apps running in the background to clean up system memory management? Is this like the situation - sometimes, when app just goes to background for a while and then launch again, the app will launch like never run before. But somehow, with TestFlight, it'll treat this like crash?

Here is the crash log (see screenshot below) which doesn't help much to identify what causes the crash .

Thanks for any feedback.