Problems with using TOctree

Okay, so yea, I think what your constructor isn’t properly setup and calling to your AActor base classes constructor.

Try this:

In Quadrant.h

UCLASS()
class PROCEDURALTERRAIN_API AQuadrant : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	AQuadrant(const FObjectInitializer& ObjectInitializer = FObjectInitializer::Get());

	// Called when the game starts or when spawned
	virtual void BeginPlay() override;
	
	// Called every frame
	virtual void Tick( float DeltaSeconds ) override;

private:

	// TOctree<FQuadrantOctreeElement, FQuadrantOctreeSematics> Data;
	
};

In Quadrant.cpp

// Sets default values
AQuadrant::AQuadrant(const FObjectInitializer& ObjectInitializer)
 : Super(ObjectInitializer)
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

}

You need to call Super because it allows the base class to initialize all its variables properly and do any work it needs before constructing your inherited object.