Crashes when playing Slomo on NiagaraSystem with Solo and DesiredAge.

When Slomo 2 is used to speed up the process, TicksToProcess is greater than 1, which means that ManualTick is called several times during one loop. 

When playback is completed by a ManualTick in that loop, UNiagaraComponent::OnSystemComplete is called. 

If AutoDestroy is enabled, SystemInstance is released. 

Since the value of TicksToProcess is greater than or equal to 0, the loop continues as it is. 

Null reference occurs because SystemInstance has been released.

More likely to crash with Slomo 10, etc.
Licensee responds by adding a null check for SystemInstance before ManualTick.

1. Open the project attached to UDN.
2. Open and PIE Untitled.umap.
3. Press the space bar to play Niagara.

The Niagara system is played in level BP with the following settings.

• Solo mode
• Frame playback with DesiredAge
• Speeding up with Slomo 2, etc.
• Enable AutoDestroy
• GC every frame

This causes a crash because SystemInstance is null when UNiagaraComponent::TickComponent does ManualTick at the timing when NiagaraSystem finishes playing.

Assertion failed: IsValid() [Link Removed] [Line: 1109]

UnrealEditor_Engine!FActorComponentTickFunction::ExecuteTickHelper<<lambda_10bf076617bb57090176fa6605386eb8> >() [D:\P4\UE5main\Engine\Source\Runtime\Engine\Classes\GameFramework\Actor.h:4254]
UnrealEditor_Engine!FActorComponentTickFunction::ExecuteTick() [D:\P4\UE5main\Engine\Source\Runtime\Engine\Private\Components\ActorComponent.cpp:1108]
UnrealEditor_Engine!FTickFunctionTask::DoTask() [D:\P4\UE5main\Engine\Source\Runtime\Engine\Private\TickTaskManager.cpp:275]
UnrealEditor_Engine!TGraphTask<FTickFunctionTask>::ExecuteTask() [D:\P4\UE5main\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:1327]
UnrealEditor_Core!FNamedTaskThread::ProcessTasksNamedThread() [D:\P4\UE5main\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:758]
UnrealEditor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [D:\P4\UE5main\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:649]
UnrealEditor_Core!FTaskGraphCompatibilityImplementation::WaitUntilTasksComplete() [D:\P4\UE5main\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:2123]
UnrealEditor_Engine!FTickTaskSequencer::ReleaseTickGroup() [D:\P4\UE5main\Engine\Source\Runtime\Engine\Private\TickTaskManager.cpp:556]
UnrealEditor_Engine!FTickTaskManager::RunTickGroup() [D:\P4\UE5main\Engine\Source\Runtime\Engine\Private\TickTaskManager.cpp:1583]
UnrealEditor_Engine!UWorld::RunTickGroup() [D:\P4\UE5main\Engine\Source\Runtime\Engine\Private\LevelTick.cpp:771]
UnrealEditor_Engine!UWorld::Tick() [D:\P4\UE5main\Engine\Source\Runtime\Engine\Private\LevelTick.cpp:1512]
UnrealEditor_UnrealEd!UEditorEngine::Tick() [D:\P4\UE5main\Engine\Source\Editor\UnrealEd\Private\EditorEngine.cpp:2002]
UnrealEditor_UnrealEd!UUnrealEdEngine::Tick() [D:\P4\UE5main\Engine\Source\Editor\UnrealEd\Private\UnrealEdEngine.cpp:519]
UnrealEditor_Win64_DebugGame!FEngineLoop::Tick() [D:\P4\UE5main\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp:5812]
UnrealEditor_Win64_DebugGame!GuardedMain() [D:\P4\UE5main\Engine\Source\Runtime\Launch\Private\Launch.cpp:188]
UnrealEditor_Win64_DebugGame!GuardedMainWrapper() [D:\P4\UE5main\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:107]
UnrealEditor_Win64_DebugGame!LaunchWindowsStartup() [D:\P4\UE5main\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:244]
UnrealEditor_Win64_DebugGame!WinMain() [D:\P4\UE5main\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:284]
UnrealEditor_Win64_DebugGame!__scrt_common_main_seh() [d:\a01\_work\12\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
kernel32
ntdll