Reproduction steps:
1. Open the attached project.
2. Build and start "theScene" to an iOS device.
3. Wait up to 2 minutes.
- Crash.

* thread #20, name = 'BackgroundWorker', stop reason = EXC_BAD_ACCESS (code=257, address=0x41)
frame #0: 0x0000000000000041
* frame #1: 0x0000000100a3d550 awsioscrashrepro`::Job_ExecuteUnityWebRequest() at UnityWebRequestProto.h:222 [opt]
frame #2: 0x00000001008c44f4 awsioscrashrepro`::Exec() [inlined] ExecuteJobFunc at JobQueue.cpp:413 [opt]
frame #3: 0x00000001008c44e0 awsioscrashrepro`::Exec() at JobQueue.cpp:476 [opt]
frame #4: 0x00000001008c4438 awsioscrashrepro`::Steal() at JobQueue.cpp:617 [opt]
frame #5: 0x00000001008c486c awsioscrashrepro`::ExecuteJobFromQueue() at JobQueue.cpp:814 [opt]
frame #6: 0x00000001008c4918 awsioscrashrepro`::ProcessJobs() at JobQueue.cpp:867 [opt]
frame #7: 0x00000001008c3f40 awsioscrashrepro`::WorkLoop() at JobQueue.cpp:937 [opt]
frame #8: 0x0000000100931548 awsioscrashrepro`::RunThreadWrapper() at Thread.cpp:36 [opt]
frame #9: 0x0000000182e4968c libsystem_pthread.dylib`_pthread_body + 240
frame #10: 0x0000000182e4959c libsystem_pthread.dylib`_pthread_start + 284
frame #11: 0x0000000182e46cb4 libsystem_pthread.dylib`thread_start + 4

Reproduced with:
iPhone 7+ iOS 10.3.2, iPad Mini 4 iOS 9.2.1
2017.3.0b3, 2017.4.1f1, 2018.1.0b13

Not reproducible with:
Android
or
2017.2.2p3, 2017.3.0a1

Note:
Case 1005678 has a similar stack trace.