If some people want to fix it, you need to edit the engine source :
void ABoxReflectionCapture::EditorApplyScale(const FVector& DeltaScale, const FVector* PivotLocation, bool bAltDown, bool bShiftDown, bool bCtrlDown)
{
UBoxReflectionCaptureComponent* BoxComponent = Cast<UBoxReflectionCaptureComponent>(GetCaptureComponent());
check(BoxComponent);
const FVector ModifiedScale = DeltaScale * ( AActor::bUsePercentageBasedScaling ? 5000.0f : 50.0f );
FVector NewScale = BoxComponent->GetRelativeScale3D() + ModifiedScale;
BoxComponent->SetRelativeScale3D(NewScale);
GetCaptureComponent()->InvalidateLightingCache();
PostEditChange();
}
in reflectioncapturecomponent.cpp, of course, add the signature to the .h.