This Mac crash originally occurred in 4.15 around March 2017, then decreased in frequency during 4.16 and 4.17. It may be starting to trend again in 4.18. There is one record of this occurring in 4.13 (in July 2017) and no records for 4.14.
According to logs, an Ensure occurs prior to the crash.
Ensure condition failed: Lhs.CurrentNum == Lhs.InitialNum [File:Runtime/Core/Public/Containers/Array.h] [Line: 206]
I've identified two different error messages that occur with this callstack.
1. SIGSEGV: invalid attempt to access memory at address 0x6f00000069
2. SIGBUS: invalid attempt to access memory at address 0x1709df4c0
User Descriptions
Callstack from Log
[2017.10.27-12.02.54:645][961]LogStaticLightingSystem: Running Lightmass w/ Mapping debug paddings DISABLED [2017.10.27-12.02.54:657][961]Cmd: MAP CHECK DONTDISPLAYDIALOG [2017.10.27-12.02.54:657][961]MapCheck: New page: Untitled_2 - Oct 28, 2017, 4:02:54 AM [2017.10.27-12.02.54:658][961]MapCheck: Error: WorldSettings Maps need lighting rebuilt [2017.10.27-12.02.54:688][961]MapCheck: Map check complete: 1 Error(s), 0 Warning(s), took 30.612ms to complete. [2017.10.27-12.02.54:689][961]LogEditorBuildUtils: Build time 0:00 [2017.10.27-12.03.00:130][100]LogStats: FPlatformStackWalk::StackWalkAndDump - 0.012 s [2017.10.27-12.03.00:130][100]LogOutputDevice: Error: === Handled ensure: === [2017.10.27-12.03.00:131][100]LogOutputDevice: Error: [2017.10.27-12.03.00:131][100]LogOutputDevice: Error: Ensure condition failed: Lhs.CurrentNum == Lhs.InitialNum [File:Runtime/Core/Public/Containers/Array.h] [Line: 206] [2017.10.27-12.03.00:131][100]LogOutputDevice: Error: Array has changed during ranged-for iteration! [2017.10.27-12.03.00:131][100]LogOutputDevice: Error: Stack: [2017.10.27-12.03.00:131][100]LogOutputDevice: Error: [Callstack] 0x003d938d UE4Editor-Core.dylib!FDebug::OptionallyLogFormattedEnsureMessageReturningFalse(bool, char const*, char const*, int, wchar_t const*, ...) [UnknownFile]) [2017.10.27-12.03.00:131][100]LogOutputDevice: Error: [Callstack] 0x06075d1e UE4Editor-Slate.dylib!PrepassWindowAndChildren(TSharedRef<SWindow, (ESPMode)0>) [UnknownFile]) [2017.10.27-12.03.00:132][100]LogOutputDevice: Error: [Callstack] 0x0607515c UE4Editor-Slate.dylib!FSlateApplication::DrawPrepass(TSharedPtr<SWindow, (ESPMode)0>) [UnknownFile]) [2017.10.27-12.03.00:132][100]LogOutputDevice: Error: [Callstack] 0x0607166d UE4Editor-Slate.dylib!FSlateApplication::PrivateDrawWindows(TSharedPtr<SWindow, (ESPMode)0>) [UnknownFile]) [2017.10.27-12.03.00:132][100]LogOutputDevice: Error: [Callstack] 0x06071172 UE4Editor-Slate.dylib!FSlateApplication::DrawWindows() [UnknownFile]) [2017.10.27-12.03.00:132][100]LogOutputDevice: Error: [Callstack] 0x0607a32d UE4Editor-Slate.dylib!FSlateApplication::TickApplication(ESlateTickType, float) [UnknownFile]) [2017.10.27-12.03.00:132][100]LogOutputDevice: Error: [Callstack] 0x060782d6 UE4Editor-Slate.dylib!FSlateApplication::Tick(ESlateTickType) [UnknownFile]) [2017.10.27-12.03.00:132][100]LogOutputDevice: Error: [Callstack] 0x0001ef9e UE4Editor!FEngineLoop::Tick() [UnknownFile]) [2017.10.27-12.03.00:132][100]LogOutputDevice: Error: [Callstack] 0x00026e62 UE4Editor!GuardedMain(wchar_t const*) [UnknownFile]) [2017.10.27-12.03.00:133][100]LogOutputDevice: Error: [Callstack] 0x00034500 UE4Editor!-[UE4AppDelegate runGameThread:] [UnknownFile]) [2017.10.27-12.03.00:133][100]LogOutputDevice: Error: [Callstack] 0x00359137 UE4Editor-Core.dylib!-[FCocoaGameThread main] [UnknownFile]) [2017.10.27-12.03.00:133][100]LogOutputDevice: Error: [Callstack] 0xbc4878ad Foundation!__NSThread__start__() [UnknownFile]) [2017.10.27-12.03.00:133][100]LogOutputDevice: Error: [Callstack] 0x09bf8b90 libsystem_pthread.dylib!_pthread_body() [UnknownFile]) [2017.10.27-12.03.00:133][100]LogOutputDevice: Error: [Callstack] 0x09bf8adc libsystem_pthread.dylib!_pthread_body() [UnknownFile]) [2017.10.27-12.03.00:133][100]LogOutputDevice: Error: [Callstack] 0x09bf82c5 libsystem_pthread.dylib!thread_start() [UnknownFile]) [2017.10.27-12.03.00:134][100]LogOutputDevice: Error: [2017.10.27-12.03.00:136][100]LogStats: SubmitErrorReport - 0.000 s [2017.10.27-12.03.06:972][100]LogStats: SendNewReport - 6.836 s [2017.10.27-12.03.06:972][100]LogStats: FDebug::EnsureFailed - 6.855 s [2017.10.27-12.03.07:037][100]LogMac: === Critical error: === SIGSEGV: invalid attempt to access memory at address 0x6f00000069 [2017.10.27-12.03.07:037][100]LogMac: 0x06075e31 UE4Editor-Slate.dylib!PrepassWindowAndChildren(TSharedRef<SWindow, (ESPMode)0>) [UnknownFile]) 0x0607515c UE4Editor-Slate.dylib!FSlateApplication::DrawPrepass(TSharedPtr<SWindow, (ESPMode)0>) [UnknownFile]) 0x0607166d UE4Editor-Slate.dylib!FSlateApplication::PrivateDrawWindows(TSharedPtr<SWindow, (ESPMode)0>) [UnknownFile]) 0x06071172 UE4Editor-Slate.dylib!FSlateApplication::DrawWindows() [UnknownFile]) 0x0607a32d UE4Editor-Slate.dylib!FSlateApplication::TickApplication(ESlateTickType, float) [UnknownFile]) 0x060782d6 UE4Editor-Slate.dylib!FSlateApplication::Tick(ESlateTickType) [UnknownFile]) 0x0001ef9e UE4Editor!FEngineLoop::Tick() [UnknownFile]) 0x00026e62 UE4Editor!GuardedMain(wchar_t const*) [UnknownFile]) 0x00034500 UE4Editor!-[UE4AppDelegate runGameThread:] [UnknownFile]) 0x00359137 UE4Editor-Core.dylib!-[FCocoaGameThread main] [UnknownFile]) 0xbc4878ad Foundation!__NSThread__start__() [UnknownFile]) 0x09bf8b90 libsystem_pthread.dylib!_pthread_body() [UnknownFile]) 0x09bf8adc libsystem_pthread.dylib!_pthread_body() [UnknownFile]) 0x09bf82c5 libsystem_pthread.dylib!thread_start() [UnknownFile])
repro steps currently unknown. One user description describes the crash as occurring while working with the Blueprint editor
BUS_ADRERR at 0x1709df4c0 ???!Unknown() UE4Editor-Slate.dylib!PrepassWindowAndChildren(TSharedRef<SWindow,() UE4Editor-Slate.dylib!FSlateApplication::DrawPrepass(TSharedPtr<SWindow,() UE4Editor-Slate.dylib!FSlateApplication::PrivateDrawWindows(TSharedPtr<SWindow,() UE4Editor-Slate.dylib!FSlateApplication::DrawWindows() UE4Editor-Slate.dylib!FSlateApplication::TickApplication() UE4Editor-Slate.dylib!FSlateApplication::Tick() UE4Editor!FEngineLoop::Tick() UE4Editor!GuardedMain() UE4Editor!<Unknown> UE4Editor-Core.dylib!<Unknown> Foundation!Unknown() libsystem_pthread.dylib!<Unknown> libsystem_pthread.dylib!<Unknown> libsystem_pthread.dylib!<Unknown>
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-51711 in the post.