firebase-ios-sdk: GULNetworkURLSession crash

Environment

Xcode version: 10.2 Firebase/Google Pod Instal log:

Using Firebase (6.2.0)
Using FirebaseABTesting (3.0.0)
Using FirebaseAnalytics (6.0.1)
Using FirebaseAnalyticsInterop (1.2.0)
Using FirebaseCore (6.0.2)
Using FirebaseDynamicLinks (4.0.0)
Using FirebaseInstanceID (4.1.1)
Using FirebaseMLCommon (0.16.0)
Using FirebaseMLVision (0.16.0)
Using FirebaseMLVisionBarcodeModel (0.16.0)
Using FirebasePerformance (3.0.0)
Using FirebaseRemoteConfig (4.0.0)

Using GTMSessionFetcher (1.2.2)
Using GoogleAPIClientForREST (1.3.9)
Using GoogleAnalytics (3.17.0)
Using GoogleAppMeasurement (6.0.1)
Using GoogleMobileVision (1.6.0)
Using GoogleSymbolUtilities (1.1.2)
Using GoogleTagManager (7.1.2)
Using GoogleToolboxForMac (2.2.1)
Using GoogleUtilities (6.2.0)
Using GoogleUtilitiesLegacy (1.3.2)

Problem

App crashes in GULNetworkURLSession, line 172. Code:

Steps to reproduce

We cannot reproduce it but about 8k users are affected.

Crash log from Firebase Crashlytics:

Fatal Exception: NSInvalidArgumentException
0  CoreFoundation                 0x181a75d04 __exceptionPreprocess
1  libobjc.A.dylib                0x180cc4528 objc_exception_throw
2  CoreFoundation                 0x181a831c8 __methodDescriptionForSelector
3  CoreFoundation                 0x181a7b6b0 ___forwarding___
4  CoreFoundation                 0x18196101c _CF_forwarding_prep_0
5  libobjc.A.dylib                0x180cc543c CALLING_SOME_+initialize_METHOD
6  libobjc.A.dylib                0x180cc5804 _class_initialize
7  libobjc.A.dylib                0x180ce0c34 objc_loadWeakRetained
8  libobjc.A.dylib                0x180ce0d3c objc_loadWeak
9  Foundation                     0x18239daa4 readARCWeakAt
10 Foundation                     0x1823854dc -[NSConcreteMapTable grow]
11 Foundation                     0x182365bc0 -[NSConcreteMapTable setObject:forKey:]
12 GoogleUtilities                0x101fa199c +[GULNetworkURLSession setSessionInFetcherMap:forSessionID:] (GULNetworkURLSession.m:699)
13 GoogleUtilities                0x101f9f688 -[GULNetworkURLSession sessionIDFromAsyncPOSTRequest:completionHandler:] (GULNetworkURLSession.m:172)
14 GoogleUtilities                0x101f9d744 -[GULNetwork postURL:payload:queue:usingBackgroundSession:completionHandler:] (GULNetwork.m:143)
15 XXXXX                       0x10418a668 -[FIRClearcutLogger sendNextPendingRequestWithCompletionHandler:]
16 XXXXX                       0x10418a8d0 __65-[FIRClearcutLogger sendNextPendingRequestWithCompletionHandler:]_block_invoke
17 libdispatch.dylib              0x1813f9088 _dispatch_call_block_and_release
18 libdispatch.dylib              0x1813f9048 _dispatch_client_callout
19 libdispatch.dylib              0x181406378 _dispatch_root_queue_drain
20 libdispatch.dylib              0x181405f10 _dispatch_worker_thread3
21 libsystem_pthread.dylib        0x18169f120 _pthread_wqthread
22 libsystem_pthread.dylib        0x18169ec20 start_wqthread

TagManagerContainerQueue
0  JavaScriptCore                 0x1ba9b1160 Inspector::JSGlobalObjectInspectorController::JSGlobalObjectInspectorController(JSC::JSGlobalObject&) + 906
1  JavaScriptCore                 0x1bac53af8 JSC::JSGlobalObject::init(JSC::VM&) + 268
2  JavaScriptCore                 0x1bac6b3c4 JSC::JSGlobalObject::finishCreation(JSC::VM&) + 104
3  JavaScriptCore                 0x1bac6b320 JSC::JSGlobalObject::create(JSC::VM&, JSC::Structure*) + 160
4  JavaScriptCore                 0x1ba4e93f4 JSGlobalContextCreateInGroup + 316
5  JavaScriptCore                 0x1ba2a05e8 -[JSContext initWithVirtualMachine:] + 108
6  VinID                          0x100eb2728 -[TAGRuntime initWithContainerId:resource:hitStore:dispatchScheduler:] + 4311426856
7  VinID                          0x100ea8d38 __55-[TAGContainer handleLoadOfContainerData:errorMessage:]_block_invoke + 4311387448
8  libdispatch.dylib              0x1b2bd0a38 _dispatch_call_block_and_release + 24
9  libdispatch.dylib              0x1b2bd17d4 _dispatch_client_callout + 16
10 libdispatch.dylib              0x1b2b7a320 _dispatch_lane_serial_drain$VARIANT$mp + 592
11 libdispatch.dylib              0x1b2b7ae3c _dispatch_lane_invoke$VARIANT$mp + 428
12 libdispatch.dylib              0x1b2b834a8 _dispatch_workloop_worker_thread + 596
13 libsystem_pthread.dylib        0x1b2db1114 _pthread_wqthread + 304
14 libsystem_pthread.dylib        0x1b2db3cd4 start_wqthread + 4


GULMutableDictionary
0  libsystem_kernel.dylib         0x1b2d2e9d4 __ulock_wait + 8
1  libsystem_platform.dylib       0x1b2d9f348 _os_unfair_lock_lock_slow + 220
2  libobjc.A.dylib                0x1b2384604 objc_destroyWeak + 144
3  libobjc.A.dylib                0x1b236a7cc object_cxxDestructFromClass(objc_object*, objc_class*) + 148
4  libobjc.A.dylib                0x1b237a6b8 objc_destructInstance + 68
5  libobjc.A.dylib                0x1b237a720 object_dispose + 16
6  GoogleUtilities                0x1018aec4c -[GULObjectSwizzler dealloc] (GULObjectSwizzler.m:155)
7  libobjc.A.dylib                0x1b2380754 _object_remove_assocations + 468
8  libobjc.A.dylib                0x1b237a6d4 objc_destructInstance + 96
9  libobjc.A.dylib                0x1b237a720 object_dispose + 16
10 libdispatch.dylib              0x1b2bd0a38 _dispatch_call_block_and_release + 24
11 libdispatch.dylib              0x1b2bd17d4 _dispatch_client_callout + 16
12 libdispatch.dylib              0x1b2b7a320 _dispatch_lane_serial_drain$VARIANT$mp + 592
13 libdispatch.dylib              0x1b2b7ae3c _dispatch_lane_invoke$VARIANT$mp + 428
14 libdispatch.dylib              0x1b2b834a8 _dispatch_workloop_worker_thread + 596
15 libsystem_pthread.dylib        0x1b2db1114 _pthread_wqthread + 304
16 libsystem_pthread.dylib        0x1b2db3cd4 start_wqthread + 4