Set Sound Submix Objectでクラッシュすることがあります。

Set Sound Submix ObjectでSubmixを変更しようとしています。
Set Sound Submix Object では添付のash_00.jpgの①の部分のSubmixを変更しようとしていますが
②の部分にSubmixがセットされている状態で同じSubmixをSet Sound Submix Object で
セットしようとするとクラッシュします。クラッシュレポートも下記に掲載しておきます。
ご確認宜しくお願い致します。

LoginId:5accde094c6b8a0a66c28aa141c36e27
EpicAccountId:92d1bdb02cb746b1a939a9105686d813

Assertion failed: Pair != nullptr [File:C:\UE\Engine\Source\Runtime\Core\Public\Containers/Map.h] [Line: 467]

UE4Editor_Core!FDebug::AssertFailed() [c:\ue\engine\source\runtime\core\private\misc\assertionmacros.cpp:425]
UE4Editor_AudioMixer!Audio::FMixerSubmix::RemoveSourceVoice() [c:\ue\engine\source\runtime\audiomixer\private\audiomixersubmix.cpp:214]
UE4Editor_AudioMixer!Audio::FMixerSourceManager::ReleaseSource() [c:\ue\engine\source\runtime\audiomixer\private\audiomixersourcemanager.cpp:351]
UE4Editor_AudioMixer!Audio::FMixerSourceManager::PumpCommandQueue() [c:\ue\engine\source\runtime\audiomixer\private\audiomixersourcemanager.cpp:2132]
UE4Editor_AudioMixer!Audio::FMixerSourceManager::ComputeNextBlockOfSamples() [c:\ue\engine\source\runtime\audiomixer\private\audiomixersourcemanager.cpp:2062]
UE4Editor_AudioMixer!Audio::FMixerDevice::OnProcessAudioStream() [c:\ue\engine\source\runtime\audiomixer\private\audiomixerdevice.cpp:441]
UE4Editor_AudioMixer!Audio::FOutputBuffer::MixNextBuffer() [c:\ue\engine\source\runtime\audiomixer\private\audiomixer.cpp:128]
UE4Editor_AudioMixer!Audio::IAudioMixerPlatformInterface::RunInternal() [c:\ue\engine\source\runtime\audiomixer\private\audiomixer.cpp:483]
UE4Editor_AudioMixer!Audio::IAudioMixerPlatformInterface::Run() [c:\ue\engine\source\runtime\audiomixer\private\audiomixer.cpp:508]
UE4Editor_Core!FRunnableThreadWin::Run() [c:\ue\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:76]

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Thanks