Async loaded material not working

Development Programming & Scripting C++
1 
...
Handle = StreamableManager.RequestAsyncLoad(SoftObjectPathA, FStreamableDelegate::CreateUObject(this, &AwindowsFunctions::afterLoading));
...

//AwindowsFunctions::afterLoading() {
	Handle->GetLoadedAssets(myObj);
	USkeletalMesh* Mesh = Cast<USkeletalMesh>(myObj[6]);
	UMaterial* Mat = Cast<UMaterial>(myObj[4]);
	if (Mat) {
		GEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Yellow, TEXT("Material Loaded."));
	}
	FSkeletalMaterial SKMat = UMaterialInstanceDynamic::Create(Mat,this);
	UMaterialInstanceDynamic* ExampleMID = UMaterialInstanceDynamic::Create(Mat,this);
	GEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Yellow, Mat->GetFName().ToString());
	MatA.Add(SKMat);
	MatA.Add(SKMat);
	if (Mesh) {
		theMesh = Mesh;
		theMesh->SetMaterials(MatA);
		SKMComp->SetSkeletalMesh(Mesh,false);
		SMComp->SetMaterial(0,Mat);
		UMaterialInterface *MatTest = SMComp->GetMaterial(0);

		GEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Red, MatTest->GetFullName());
		GEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Red, MatTest->GetFName().ToString());

	}
...

I mounted a customed Pak file to a customed mountpoint. The Skeleton mesh loaded worked. But the material just didn’t work, no matter how. However, printing the name of it shows it had been loaded properly. I’m so confused. Pls, somebody help me…