Unreal Engine Issues and Bug Tracker (UE-81818)

Description

In a Level Streaming setup, unloading a level that has spawned an AI Character with a Detour AI Controller causes a crash.

This was reported and tested in 4.23 (CL-8386587). This was reproduced in 4.22.3 (CL-7053642) and 4.24 (CL-9551884)

Steps to Reproduce

Open the UE4 Editor and create a new Third Person project
Create a new level for streaming and place a Nav Mesh Bounds inside it
Assign streaming level to persistent level
Create new character and create AI controller from parent class DetourCrowdAIController
Assign this AI controller to the created Character
Add spawning this character in streaming level (Begin play)
Add logic loading and unloading streaming level in level blueprint of persistent level (Event key or begin play with delay).
Play in editor, wait for the streaming level to load and spawn the character, then unload the streaming level

Results: Crash in UE4Editor_AIModule, UE4Editor_NavigationSystem

Expected: No Crash

Callstack

[2019.10.14-17.40.27:819][288]LogWindows: Error: === Critical error: ===
[2019.10.14-17.40.27:819][288]LogWindows: Error: 
[2019.10.14-17.40.27:819][288]LogWindows: Error: Fatal error!
[2019.10.14-17.40.27:819][288]LogWindows: Error: 
[2019.10.14-17.40.27:819][288]LogWindows: Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x00000000
[2019.10.14-17.40.27:819][288]LogWindows: Error: 
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ffc6f5b265e UE4Editor-AIModule.dll!UCrowdManager::Tick() [d:\build\++ue4\sync\engine\source\runtime\aimodule\private\navigation\crowdmanager.cpp:235]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ffc7884cd59 UE4Editor-NavigationSystem.dll!UNavigationSystemV1::Tick() [d:\build\++ue4\sync\engine\source\runtime\navigationsystem\private\navigationsystem.cpp:1025]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ffc71af0d65 UE4Editor-Engine.dll!UWorld::Tick() [d:\build\++ue4\sync\engine\source\runtime\engine\private\leveltick.cpp:1470]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ffc8d0ce00b UE4Editor-UnrealEd.dll!UEditorEngine::Tick() [d:\build\++ue4\sync\engine\source\editor\unrealed\private\editorengine.cpp:1638]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ffc8d924b16 UE4Editor-UnrealEd.dll!UUnrealEdEngine::Tick() [d:\build\++ue4\sync\engine\source\editor\unrealed\private\unrealedengine.cpp:407]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ff69b5d7b0a UE4Editor.exe!FEngineLoop::Tick() [d:\build\++ue4\sync\engine\source\runtime\launch\private\launchengineloop.cpp:4257]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ff69b5ea91c UE4Editor.exe!GuardedMain() [d:\build\++ue4\sync\engine\source\runtime\launch\private\launch.cpp:173]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ff69b5ea9fa UE4Editor.exe!GuardedMainWrapper() [d:\build\++ue4\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:147]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ff69b5fb92c UE4Editor.exe!WinMain() [d:\build\++ue4\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:279]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ff69b5fe60e UE4Editor.exe!__scrt_common_main_seh() [d:\agent\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ffccbda37e4 KERNEL32.DLL!UnknownFunction []
[2019.10.14-17.40.27:819][288]LogWindows: Error: [Callstack] 0x00007ffcce91cb81 ntdll.dll!UnknownFunction []

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Fixed

Component	UE - AI
Affects Versions	4.23, 4.24, 4.22.3
Target Fix	4.24

Fix Commit	9676135
Main Commit	9676136
Release Commit	9676135

Created	Oct 14, 2019
Resolved	Oct 18, 2019
Updated	Jan 25, 2021

UE-81818

Unloading a spawned Detour AI Controller using Level Streaming causes a crash

Unloading a spawned Detour AI Controller using Level Streaming causes a crash

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