Description

When repeatedly loading and unloading sublevels with a NavBoundsVolume, it will cause a crash when using a NavModifierVolume. When the NavMesh is unloaded, it seems that the number of the DirtyLayers array is sometimes smaller than that of the CompressedLayers array.

This was reported in 4.20 (CL-4212847) and tested in Main 4.21 (CL-4221482)

Steps to Reproduce
  1. Download the attached project
  2. Open "1000x1000x200_Div.umap".
  3. # Press Play
  4. Step on the trigger box named "LoadLandscape"
  5. Step on the trigger box named "LoadSomeNAVs"
  6. Press 1 on the keyboard to unload the NavMesh.
  7. Execute steps 5 and 6 repeatedly

Results: The Editor crashes

Expected: The Editor doesn't crash

Callstack
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007ff80e2f3fb8 KERNELBASE.dll!UnknownFunction []
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007ffff4b76850 UE4Editor-ApplicationCore.dll!FWindowsErrorOutputDevice::Serialize() [d:\build\++ue4\sync\engine\source\runtime\applicationcore\private\windows\windowserroroutputdevice.cpp:65]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffcc4962ec UE4Editor-Core.dll!FOutputDevice::LogfImpl() [d:\build\++ue4\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:70]
[2018.07.19-17.23.41:846][121]LogWindows: Error: HandleError re-entered.
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffcc4251cb UE4Editor-Core.dll!FDebug::AssertFailed() [d:\build\++ue4\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:425]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffc49823ed UE4Editor-NavigationSystem.dll!FRecastTileGenerator::GenerateNavigationData() [d:\build\++ue4\sync\engine\source\runtime\navigationsystem\private\navmesh\recastnavmeshgenerator.cpp:2585]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffc49834bd UE4Editor-NavigationSystem.dll!FRecastTileGenerator::GenerateTile() [d:\build\++ue4\sync\engine\source\runtime\navigationsystem\private\navmesh\recastnavmeshgenerator.cpp:2202]
[2018.07.19-17.23.41:846][121]LogWindows: FPlatformMisc::RequestExit(1)
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffc494e294 UE4Editor-NavigationSystem.dll!FRecastTileGenerator::DoWork() [d:\build\++ue4\sync\engine\source\runtime\navigationsystem\private\navmesh\recastnavmeshgenerator.cpp:1680]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffc494e0c1 UE4Editor-NavigationSystem.dll!FAsyncTask<FRecastTileGeneratorWrapper>::DoWork() [d:\build\++ue4\sync\engine\source\runtime\core\public\async\asyncwork.h:264]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffc494df1e UE4Editor-NavigationSystem.dll!FAsyncTask<FRecastTileGeneratorWrapper>::DoThreadedWork() [d:\build\++ue4\sync\engine\source\runtime\core\public\async\asyncwork.h:288]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffcc3838a5 UE4Editor-Core.dll!FQueuedThread::Run() [d:\build\++ue4\sync\engine\source\runtime\core\private\hal\threadingbase.cpp:455]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffcc6f6abc UE4Editor-Core.dll!FRunnableThreadWin::Run() [d:\build\++ue4\sync\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:76]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007fffcc6f1707 UE4Editor-Core.dll!FRunnableThreadWin::GuardedRun() [d:\build\++ue4\sync\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:33]
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007ff80fca1fe4 KERNEL32.DLL!UnknownFunction []
[2018.07.19-17.23.41:846][121]LogWindows: Error: [Callstack] 0x00007ff81145ef91 ntdll.dll!UnknownFunction

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Cannot Reproduce
ComponentUE - AI
Affects Versions4.204.21
Target Fix4.21
CreatedJul 19, 2018
ResolvedOct 9, 2018
UpdatedOct 9, 2018
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