Hello everyone! Faced with the same problem.
Assertion failed: SerializeNum >= 0 [File:Runtime/Core/Public/Containers/Array.h] [Line: 1253]
If it appears on iOS, it means that in your scene there is an object which has a property FVector. On other platforms FVector is typedefed to UE::Math::TVector, but on iOS it is defined through FVectorWorkaround. And if you try to read the scene, it crashes. I’ve replaced the property by FVector3d) I hope it will help someone.