memory leak when use UInstancedStaticMeshComponent

Here is the problem code: .h // Fill out your copyright notice in the Description page of Project Settings.

 #pragma once
 
 #include "CoreMinimal.h"
 #include "GameFramework/Actor.h"
 #include "Components/InstancedStaticMeshComponent.h"
 #include "MyActorForISMTest.generated.h"
 
 UCLASS()
 class ISMTEST_API AMyActorForISMTest : public AActor
 {
     GENERATED_BODY()
 
         UPROPERTY(EditAnywhere, Category = "test")
         AActor * myObj;
 
 public: 
     TMap<size_t, UInstancedStaticMeshComponent *> mapForISMC; 
     TArray <size_t> arrayHaveColor; 
     int totalNum;
 public:    
     // Sets default values for this actor's properties
     AMyActorForISMTest();
 
 protected:
     // Called when the game starts or when spawned
     virtual void BeginPlay() override;
 
 public:    
     // Called every frame
     virtual void Tick(float DeltaTime) override;
 
     
     
 };

.cpp

 // Fill out your copyright notice in the Description page of Project Settings.
 
 #include "MyActorForISMTest.h"
 
 
 // Sets default values
 AMyActorForISMTest::AMyActorForISMTest()
 {
      // 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;
     totalNum = 3000;
 
 }
 
 // Called when the game starts or when spawned
 void AMyActorForISMTest::BeginPlay()
 {
     Super::BeginPlay();
     
     UWorld* World = myObj->GetWorld();
     UClass * muClass = myObj->GetClass();
 
     for (size_t i = 0; i < totalNum; i++)
     { 
         AActor* actorPtr = World->SpawnActor<AActor>(muClass, FVector(0, 0, 0), FVector(0, 0, 0).Rotation());
         actorPtr->AttachToActor(this, FAttachmentTransformRules(EAttachmentRule::KeepWorld, false)); 
         actorPtr->SetOwner(this);
         UStaticMeshComponent* mCube = actorPtr->FindComponentByClass<UStaticMeshComponent>();
         mCube->SetMobility(EComponentMobility::Static); 
         UMaterialInstanceDynamic* mMaterial = UMaterialInstanceDynamic::Create(mCube->GetMaterial(0), NULL); 
         mCube->SetMaterial(0, mMaterial); 
         mapForISMC.Add(i, actorPtr->FindComponentByClass<UInstancedStaticMeshComponent>()); 
     } 
 }
 
 // Called every frame
 void AMyActorForISMTest::Tick(float DeltaTime)
 {
     Super::Tick(DeltaTime);
 
     arrayHaveColor.Empty();
     for (size_t i = 0; i < totalNum; i++)
     {
         mapForISMC[i]->ClearInstances();
     }
 
     for (size_t i = 0; i < totalNum; i++)
     { 
         arrayHaveColor.Add(i);
     }
      
     for (size_t i = 0; i < totalNum; i++)
     {
         size_t tempIndex = arrayHaveColor[i];
         FInstancedStaticMeshInstanceData insData;  
         mapForISMC[i]->PerInstanceSMData.Add(insData);     
     }  
 }
 

That will cause memory leak.Because too many InstancedStaticMeshComponent need update in Tick function.After I put all insData in one InstancedStaticMeshComponent,problem solved.But the reason detail still unclear for me.