How to reproduce:
1. Open the attached UnityAdTest.zip project
2. Build for iOS and deploy the Xcode project to the device
3. Click on the button show ad to initialize ad
4. Click on the same button to show the video ad
====Crash occurs====

Reproducible with: 2020.2.0a12, 2020.2.0a16

Not reproducible with: 2019.3.16f1, 2019.4.3f1, 2020.1.0b15, 2020.2.0a11

Reproducible with:
iPad 7th gen (iOS 13.2.2)
iPhone 7 (iOS 12.3.1)

Could not test on:
N/A, Samsung Galaxy S9 (SM-G960F), Android 8.0.0, CPU: Exynos 9 Series 9810, GPU: Mali-G72
VLNQA00313, Huawei Y6 Ⅱ Compact (HUAWEI LYO-L01), Android 5.1, CPU: MediaTek MT6735, GPU: Mali-T720

Android logcat is outputting this error whenever I press the "Show Ad" button:
2020/07/08 13:43:31.586 30651 30709 Error UnityAds com.unity3d.services.ads.UnityAdsImplementation.handleShowError() (line:265) :: Unity Ads show failed: Unity Ads default placement is not initialized

Stack trace:
frame #0: 0x000000019c2cbec4 libsystem_kernel.dylib`__pthread_kill + 8
frame #1: 0x000000019c1e7774 libsystem_pthread.dylib`pthread_kill$VARIANT$mp + 112
frame #2: 0x000000019c13b844 libsystem_c.dylib`abort + 100
frame #3: 0x000000019c2947d4 libc++abi.dylib`abort_message + 128
frame #4: 0x000000019c2949c4 libc++abi.dylib`demangling_terminate_handler() + 296
frame #5: 0x000000019c1fc258 libobjc.A.dylib`_objc_terminate() + 124
frame #6: 0x000000019c2a1304 libc++abi.dylib`std::__terminate(void (*)()) + 16
frame #7: 0x000000019c2a129c libc++abi.dylib`std::terminate() + 44
frame #8: 0x000000019c1fc1dc libobjc.A.dylib`objc_terminate + 12
frame #9: 0x000000019c1a1198 libdispatch.dylib`_dispatch_client_callout + 36
frame #10: 0x000000019c153190 libdispatch.dylib`_dispatch_main_queue_callback_4CF$VARIANT$mp + 1044
frame #11: 0x000000019c4513a8 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 12
frame #12: 0x000000019c44c39c CoreFoundation`__CFRunLoopRun + 2004
frame #13: 0x000000019c44b8a0 CoreFoundation`CFRunLoopRunSpecific + 464
frame #14: 0x00000001a63a3328 GraphicsServices`GSEventRunModal + 104
frame #15: 0x00000001a053c740 UIKitCore`UIApplicationMain + 1936
frame #16: 0x0000000104018414 UnityFramework`-[UnityFramework runUIApplicationMainWithArgc:argv:] + 108
* frame #17: 0x00000001023a3e1c samavanDefender`main(argc=<unavailable>, argv=<unavailable>) at main.mm:26:9 [opt]
frame #18: 0x000000019c2d6360 libdyld.dylib`start + 4