Crash in some pointer

[hijamoya]

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Issue Description

What

We keep receiving some crash after upgrade to 6.0.0. The latest version 6.2.1 has the issue, too.

Here is the trace:

0  libobjc.A.dylib         _objc_retain
1  Kingfisher              0x1dac4 (-0x101704000 + 4319222468)
2  Kingfisher              0x5a644 (-0x101704000 + 4319471172)
3  Kingfisher              0x823b8 (-0x101704000 + 4319634360)
4  Kingfisher              0x8d490 (-0x101704000 + 4319679632)
5  Kingfisher              0x8d584 (-0x101704000 + 4319679876)
6  CFNetwork               ___67-[NSURLSession delegate_dataTask:didReceiveData:completionHandler:]_block_invoke.264
7  Foundation              ___NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__
8  Foundation              -[NSBlockOperation main]
9  Foundation              -[__NSOperationInternal _start:]
10 libdispatch.dylib       __dispatch_client_callout
11 libdispatch.dylib       __dispatch_block_invoke_direct$VARIANT$mp
12 libdispatch.dylib       __dispatch_client_callout
13 libdispatch.dylib       __dispatch_block_invoke_direct$VARIANT$mp
14 libdispatch.dylib       _dispatch_block_perform$VARIANT$mp
15 Foundation              ___NSOQSchedule_f
16 libdispatch.dylib       __dispatch_client_callout
17 libdispatch.dylib       __dispatch_continuation_pop$VARIANT$mp
18 libdispatch.dylib       __dispatch_async_redirect_invoke$VARIANT$mp
19 libdispatch.dylib       __dispatch_root_queue_drain
20 libdispatch.dylib       __dispatch_worker_thread3
21 libsystem_pthread.dylib __pthread_wqthread

Do you have any suggestion?

Thanks!

[hijamoya]

New information is the crash only happened in iOS 11 and iOS 12