Crash on Level Reload in Standalone when Set Sound Mix Class Override is called

When the Set Sound Mix Override is called, reloading the level causes a crash when played in Standalone.

Tested in 4.19.2 (CL - 4033788), 4.20.2 (CL - 4302132), 4.21 (CL - 4324949)

1. Download and open attached project
2. Play in Standalone
3. Move towards the left

Expected: The level reloads as it does when PIE

Result: The project crashes

LoginId:5964f8f84766f4b976277180442869c1
EpicAccountId:2baa9d521a314b24b2efea04e88261b2

Assertion failed: IsValidIndex(Index) [Link Removed] [Line: 403] IsValidIndex(6357092)

UE4Editor_Core!FDebug::AssertFailed() [d:\build\++ue4\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:425]
UE4Editor_Core!FName::GetDisplayNameEntry() [d:\build\++ue4\sync\engine\source\runtime\core\private\uobject\unrealnames.cpp:934]
UE4Editor_Core!FName::ToString() [d:\build\++ue4\sync\engine\source\runtime\core\private\uobject\unrealnames.cpp:956]
UE4Editor_Core!FName::ToString() [d:\build\++ue4\sync\engine\source\runtime\core\private\uobject\unrealnames.cpp:950]
UE4Editor_Engine!FAudioDevice::RecursiveApplyAdjuster() [d:\build\++ue4\sync\engine\source\runtime\engine\private\audiodevice.cpp:1787]
UE4Editor_Engine!FAudioDevice::ApplyClassAdjusters() [d:\build\++ue4\sync\engine\source\runtime\engine\private\audiodevice.cpp:2194]
UE4Editor_Engine!FAudioDevice::UpdateSoundClassProperties() [d:\build\++ue4\sync\engine\source\runtime\engine\private\audiodevice.cpp:2298]
UE4Editor_Engine!FAudioDevice::Update() [d:\build\++ue4\sync\engine\source\runtime\engine\private\audiodevice.cpp:3496]
UE4Editor_Engine!TGraphTask<FFunctionGraphTask>::ExecuteTask() [d:\build\++ue4\sync\engine\source\runtime\core\public\async\taskgraphinterfaces.h:830]
UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() [d:\build\++ue4\sync\engine\source\runtime\core\private\async\taskgraph.cpp:665]
UE4Editor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [d:\build\++ue4\sync\engine\source\runtime\core\private\async\taskgraph.cpp:574]
UE4Editor_Engine!FAudioThread::Run() [d:\build\++ue4\sync\engine\source\runtime\engine\private\audiothread.cpp:187]
UE4Editor_Core!FRunnableThreadWin::Run() [d:\build\++ue4\sync\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:76]