For those having errors not related to Intellisense, it may be because you haven’t set an Owner for your object. When you call GetOwner its methods are null. See the declaration: AActor* GetOwner() const; Hence the pointer to incomplete class error.
// Called when the game starts or when spawned
void ASomeActor::BeginPlay()
{
Super::BeginPlay();
ASpawnHelper* OwnerObject = NewObject<ASpawnHelper>(this);
SetOwner(OwnerObject);
FString ObjectName = GetOwner()->GetName();
FString ObjectPos = GetOwner()->GetTransform().GetLocation().ToString();
GEngine->AddOnScreenDebugMessage(-1, 1000, FColor::White, FString::Printf(TEXT("Object Name: %s"), *ObjectName));
GEngine->AddOnScreenDebugMessage(-1, 1000, FColor::White, FString::Printf(TEXT("Object Pos: %s"), *ObjectPos));
}
In this example my Owner is ASpawnHelper* called OwnerObject.