Occasional crash at NSURLSessionDataTask dataTaskWithRequest:completionHandler:

Question

I have a weather app that refreshes asynchronously. While I've never seen it crash myself, I do see about a crash per day in Apple's reports, and not from a specific device. The app does have a good amount of users and it refreshes every few minutes, but I have no idea what kind of percentage send reports to Apple, so don't really know how rare the crash really is. I've tried a few things, like making sure I the Async Downloader class that creates the datatask does not get destroyed etc. There are 2 kinds of reported crashes, the most common is at this code:

-(void)startDownload
{
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:fileURL] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:12];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

    if (!session || !request || ![session respondsToSelector:@selector(dataTaskWithRequest:completionHandler:)])
        return;
    // Stack trace points to line below crashing
    self.dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {...}
    // ...
}

The "defensive" if is a sanity check as the crash stack trace looks like this:

That self.dataTask is just @property NSURLSessionDataTask *dataTask;.

Any ideas on what to look into or try in order to avoid this?

I seems quite rare overall so I am wondering if it's a case of the app is getting killed by the system or something like that which causes an unclean termination. Would welcome any suggestion though.

Edit: Couldn't find how to get Xcode to show me more info from the crash dump, but of course I could just open it with a text editor and here is all the info:

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Triggered by Thread:  9

Last Exception Backtrace:
0   CoreFoundation                  0x1ca108cb4 __exceptionPreprocess + 164 (NSException.m:202)
1   libobjc.A.dylib                 0x1c32243d0 objc_exception_throw + 60 (objc-exception.mm:356)
2   CoreFoundation                  0x1ca27dab8 -[NSObject(NSObject) doesNotRecognizeSelector:] + 136 (NSObject.m:140)
3   CoreFoundation                  0x1ca11f0e8 ___forwarding___ + 1592 (NSForwarding.m:3578)
4   CoreFoundation                  0x1ca185900 _CF_forwarding_prep_0 + 96 (:-1)
5   App                             0x1009667cc -[AsyncDownloader startDownload] + 396 (AsyncDownloader.m:79)

Now, going to the thread that triggered this:

Thread 9 name:
Thread 9 Crashed:
0   libsystem_kernel.dylib          0x0000000208743558 __pthread_kill + 8 (:-1)
1   libsystem_pthread.dylib         0x0000000229411118 pthread_kill + 268 (pthread.c:1670)
2   libsystem_c.dylib               0x00000001d162b178 abort + 180 (abort.c:118)
3   libc++abi.dylib                 0x000000022934fbf8 abort_message + 132 (:-1)
4   libc++abi.dylib                 0x000000022933f444 demangling_terminate_handler() + 348 (:-1)
5   libobjc.A.dylib                 0x00000001c3229ea4 _objc_terminate() + 144 (objc-exception.mm:498)
6   libc++abi.dylib                 0x000000022934efbc std::__terminate(void (*)()) + 16 (:-1)
7   libc++abi.dylib                 0x000000022934ef60 std::terminate() + 56 (:-1)
8   libdispatch.dylib               0x00000001d15caec0 _dispatch_client_callout + 40 (object.m:563)
9   libdispatch.dylib               0x00000001d15ce330 _dispatch_continuation_pop + 504 (queue.c:306)
10  libdispatch.dylib               0x00000001d15e1908 _dispatch_source_invoke + 1588 (source.c:961)
11  libdispatch.dylib               0x00000001d15cde6c _dispatch_queue_override_invoke + 500 (queue.c:0)
12  libdispatch.dylib               0x00000001d15dc944 _dispatch_root_queue_drain + 396 (queue.c:7051)
13  libdispatch.dylib               0x00000001d15dd158 _dispatch_worker_thread2 + 164 (queue.c:7119)
14  libsystem_pthread.dylib         0x000000022940ada0 _pthread_wqthread + 228 (pthread.c:2631)
15  libsystem_pthread.dylib         0x000000022940ab7c start_wqthread + 8 (:-1)


Thread 9 crashed with ARM Thread State (64-bit):
    x0: 0x0000000000000000   x1: 0x0000000000000000   x2: 0x0000000000000000   x3: 0x0000000000000000
    x4: 0x0000000229353647   x5: 0x000000016fa2acb0   x6: 0x000000000000006e   x7: 0x0000000000002700
    x8: 0xc5115eb4a9cc1e34   x9: 0xc5115eb5c66eae34  x10: 0x0000000000000200  x11: 0x000000000000000b
   x12: 0x000000000000000b  x13: 0x00000000001ff800  x14: 0x00000000000007fb  x15: 0x000000009002802e
   x16: 0x0000000000000148  x17: 0x000000016fa2b000  x18: 0x0000000000000000  x19: 0x0000000000000006
   x20: 0x000000000001e10f  x21: 0x000000016fa2b0e0  x22: 0x0000000000000110  x23: 0x0000000000000000
   x24: 0x0000000000000000  x25: 0x000000016fa2b0e0  x26: 0x0000000000030008  x27: 0x0000000282e3d180
   x28: 0x0000000220904c80   fp: 0x000000016fa2ac20   lr: 0x0000000229411118
    sp: 0x000000016fa2ac00   pc: 0x0000000208743558 cpsr: 0x40001000
   esr: 0x56000080  Address size fault