Deleting a Sound Cue/wave from the Content Browser that is referenced by a Matinee actor Sound Track, and attempt to play the Matinee a crash will occur.
I would expect the sound track to simply play nothing until the matinee times out.
1. Create new blank blueprint project with 'Starter Content'
2. Create a Matinee.
3. Create new Empty Group.
4. Add Sound track. Put some cue/wave here as keyframe.
5. Save level.
6. Remove referenced cue/wave from Content Browser.
7. Don't save level so matinee will end up with an empty track, showing "None" instead of file name.
8. Play this Matinee using the 'Play on Level Load' option within 'Details' panel.
10. Wait for Crash
UE4Editor_Engine! UInterpTrackSound::UpdateTrack() interpolation.cpp:7857
UE4Editor_Engine! UInterpTrack::ConditionalUpdateTrack() interpolation.cpp:2912
UE4Editor_Engine! UInterpGroup::UpdateGroup() interpolation.cpp:2035
UE4Editor_Engine! AMatineeActor::UpdateInterp() interpolation.cpp:735
UE4Editor_Engine! AMatineeActor::StepInterp() interpolation.cpp:1114
UE4Editor_Engine! AMatineeActor::Tick() interpolation.cpp:610
UE4Editor_Engine! AActor::TickActor() actor.cpp:657
UE4Editor_Engine! FActorTickFunction::ExecuteTick() actor.cpp:105
UE4Editor_Engine! FTickTaskSequencer::FTickFunctionTask::DoTask() ticktaskmanager.cpp:113
UE4Editor_Engine! TGraphTask<FTickTaskSequencer::FTickFunctionTask>::ExecuteTask() taskgraphinterfaces.h:759
UE4Editor_Core! FTaskThread::ProcessTasks() taskgraph.cpp:430
UE4Editor_Core! FTaskThread::ProcessTasksUntilQuit() taskgraph.cpp:273
UE4Editor_Core! FTaskGraphImplementation::WaitUntilTasksComplete() taskgraph.cpp:991
UE4Editor_Engine! FTaskGraphInterface::WaitUntilTaskCompletes() taskgraphinterfaces.h:192
UE4Editor_Engine! FTickTaskSequencer::ReleaseTickGroup() ticktaskmanager.cpp:232
UE4Editor_Engine! FTickTaskManager::RunTickGroup() ticktaskmanager.cpp:643
UE4Editor_Engine! UWorld::RunTickGroup() leveltick.cpp:698
UE4Editor_Engine! UWorld::Tick() leveltick.cpp:1188
UE4Editor_UnrealEd! UEditorEngine::Tick() editorengine.cpp:1341
UE4Editor_UnrealEd! UUnrealEdEngine::Tick() unrealedengine.cpp:366
UE4Editor! FEngineLoop::Tick() launchengineloop.cpp:2372
UE4Editor! GuardedMain() launch.cpp:142
UE4Editor! GuardedMainWrapper() launchwindows.cpp:126
UE4Editor! WinMain() launchwindows.cpp:295
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