Assertion failed: (Index >= 0) & (Index < ArrayNum) when importing large Alembic file

Importing alembic as skeletal mesh takes too much memory, causes TArray overflow and crashes import
...
I'm working in the team that's working on virtual movie production in unreal engine and currently we think that alembic is the best format that fit our needs
...

Currently we hit a wall with our 2 million normals mesh importing it with 800 frames, it results in critical error 
....
I've tried to rewrite AlembicImporter myself to make it fit to 64-bit size arrays and it worked, But there's issue number two - importing alembic takes too much memory. In our real life case our mesh has size of 3 GB, it has 2 million normals and 800 frames of animation. The only way we were able to import it is by increasing our RAM to 64 GB and virtual memory to 300 GB.
...

What i've learn investigating the code - it's lines like that need to have TArray replaced with TArray 64.
https://github.com/EpicGames/UnrealEngine/blob/46544fa5e0aa9e6740c19b44b0628b72e7bbd5ce/Engine/Plugins/Importers/AlembicImporter/Source/AlembicLibrary/Private/AbcImporter.cpp#L1168
But then again you'll need to also cast all 32 bit integers to 64 bit when for example in this line `NormalsMatrices[MeshIndex].AddZeroed(AverageNormalData[MeshIndex].Num() * 3 * NumSamples);` -> NormalsMatrices[MeshIndex].AddZeroed((int64) AverageNormalData[MeshIndex].Num() * 3 * NumSamples);
And then to fix the issue you'll need to rewrite all those function definitions like `AbcImporterUtilities::GenerateDeltaFrameDataMatrix` that interact somehow with TArray64. 

UnrealEditor-AlembicLibrary!AbcImporterUtilities::GenerateDeltaFrameDataMatrix(TArray<UE::Math::TVector<float>,TSizedDefaultAllocator<32> > const &,TArray<UE::Math::TVector<float>,TSizedDefaultAllocator<32> > const &,TArray<UE::Math::TVector<float>,TSizedDefaultAllocator<32> > const &,TArray<UE::Math::TVector<float>,TSizedDefaultAllocator<32> > const &,int,int,int,UE::Math::TVector<double> const &,TArray<float,TSizedDefaultAllocator<32> > &,TArray<float,TSizedDefaultAllocator<32> > &) [AbcImportUtilities.cpp:1215]
UnrealEditor-AlembicLibrary!static void <lambda_e302fdf8be2f45152e103006e42fd95d>::operator() [AbcImporter.cpp:1229]
UnrealEditor-AlembicLibrary!void UE::Core::Private::Function::TFunctionRefCaller<TFunction<void __cdecl(int,FAbcFile *) [Function.h:549]
UnrealEditor-AlembicLibrary!static void <lambda_e2c6f0a54d6a56cc0b09565c56cc3fc2>::operator() [AbcFile.cpp:565]
UnrealEditor-AlembicLibrary!`ParallelForImpl::NewParallelForInternal<TFunctionRef<void >,<lambda_600b85aa2a81f4761389a82b02631227>,std::nullptr_t>(int,TFunctionRef<void >,<lambda_600b85aa2a81f4761389a82b02631227>,EParallelForFlags,TArrayView<std::nullptr_t,int> const &) [ParallelFor.h:566]
UnrealEditor-AlembicLibrary!LowLevelTasks::TTaskDelegate<void ,48>::TTaskDelegateImpl<<lambda_a7d909f875cf8fde887b62459e73acd4>,0>::CallAndMove(LowLevelTasks::TTaskDelegate<void ,48> &,void *,unsigned int,bool) [TaskDelegate.h:171]
UnrealEditor-Core!LowLevelTasks::FTask::ExecuteTask() [Task.h:426]
UnrealEditor-Core!LowLevelTasks::FScheduler::TryExecuteTaskFrom<&LowLevelTasks::TLocalQueueRegistry<1024>::TLocalQueue::DequeueGlobal(bool,bool) [Scheduler.cpp:280]
UnrealEditor-Core!LowLevelTasks::FScheduler::WorkerMain(LowLevelTasks::FSleepEvent *,LowLevelTasks::TLocalQueueRegistry<1024>::TLocalQueue *,unsigned int,bool) [Scheduler.cpp:320]
UnrealEditor-Core!static void UE::Core::Private::Function::TFunctionRefCaller<<lambda_776551d1e343b6cb7eaf0e5521c77c81>,void __cdecl(void) [Function.h:549]
UnrealEditor-Core!FThreadImpl::Run() [Thread.cpp:69]
UnrealEditor-Core!FRunnableThreadWin::Run() [WindowsRunnableThread.cpp:146]
UnrealEditor-Core!FRunnableThreadWin::GuardedRun() [WindowsRunnableThread.cpp:76]
KERNEL32!7ffe2fe60000  + 17034
ntdll!7ffe30410000  + 52651