iOS 13 kept killing app instance after app entering background.

[su3]

[REQUIRED] Step 2: Describe your environment
Xcode version: 11 Beta 7
iOS: 13.1 (iOS 13 Beta 8 has the same issue)
Firebase SDK version: 6.7.0
Firebase Component:
Firebase: 6.7.0
Firebase/Analytics

Use cocopod like this:

pod 'Fabric'
pod 'Crashlytics'
pod 'Firebase/Analytics' '6.7.0'

[REQUIRED] Step 3: Describe the problem
iOS (13.1) kept killing app instance after app entering background.

Steps to reproduce:

1. Integrate Firebase Analytics into app like:
   FirebaseApp.configure()
   Fabric.sharedSDK().debug = false
   Fabric.with([Crashlytics.self])

    ...
    Analytics.logEvent...
   

   Build and run the app (detach XCode if it's started from XCode).

2. Put app into background (swipe up or press Home button) and turn off phone screen for several minutes.

3. Wake up the phone and tap the app icon to bring the app to foreground:
   Expected:
   The app is recovered from previous suspended state.

Got:
The previous app instance was destroyed by iOS and a new app instance is created.

If we remove all Firebase pods as well as the code referencing them from our project, we got expected results - the app is able to survive from background state.

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[morganchen12]

@su3 can you share the stack trace for the background kill?

[su3]

@morganchen12 No crash reports. No stack trace. It's like an normal termination except it just shouldn't be terminated by the OS.
Any chance it's caused by leaking background tasks inside Firebase?

[morganchen12]

That was a bug fixed recently in Firebase. Background termination should still leave a stack trace on the device, which you can access from the Devices menu in Xcode. The exception code is usually 0x8badf00d.

It's unlikely this bug is a regression of the background tasks issue since that was released relatively recently.

cc @mikehaney24

[morganchen12]

Also @su3 does this occur on iOS 12 or just 13?

[su3]

@morganchen12 It's always reproducible on iOS 13. Not an issue on 12.

[mccarron]

@su3 do you see libdyld.dylib or GULLoggingClientQueue crashes in Crashlytics (or similar?) I am getting about 10 a week right now from iOS 13 users and I think this issue is related.

It's always iOS 13 users and always the app is backgrounded.

Crashed: GULLoggingClientQueue
0  libdyld.dylib                  0x1988d7d8c <redacted> + 44
1  ???                            0x0 (Missing)
2  ???                            0x0 (Missing)
3  ???                            0x0 (Missing)
4  ???                            0x6636bc81988e2c00 (Missing)
5  ???                            0x0 (Missing)
6  ???                            0x593b0c81986cc000 (Missing)
7  ???                            0x0 (Missing)
8  ???                            0x0 (Missing)
9  libdispatch.dylib              0x198787bb0 <redacted> + 32
10 ???                            0x2a27128198789000 (Missing)
11 ???                            0x2216a1019878f400 (Missing)
12 ???                            0x7f7a440198790000 (Missing)
13 ???                            0x0 (Missing)
14 ???                            0x0 (Missing)
15 ???                            0x2302c781987f4c00 (Missing)