Crash when using VR Mode with Extra Viewports and a Camera Actor

From User:

"Normally UE4 has an "Eject" button which is great for live-debugging your app, because you can see everything that's happening in your world, and see the World Outliner in realtime while the app is running. However this button is not available when you have a VR headset plugged in. However, using the "VR Editor" button, this is possible, and I figured out steps to achieve this. But it seems unstable. If I have a camera selected when I hit "Stop" it will crash consistently."

Confirmed in 4.24 MAIN @ CL 7224837 with different callstack (.txt attached)

Confirmed with Vive and Oculus

1. Create an Empty Level
2. Place a Camera Actor in the level
3. Open an extra Viewport (Window > Viewports > Viewport 2)
4. Click inside of that Viewport and select "VR Mode"
5. Click back into your main UE4 viewport
6. Click Play > Selected Viewport
7. Eject
8. Select the camera actor
9. With the camera actor still selected click 'Stop'

Assertion failed: [Link Removed] [Line: 63] MaterialInstanceDynamic /Script/MaterialEditor.MaterialEditingLibrary:UpdateMaterialInstance.FloatProperty_-2.MaterialInstanceDynamic_2 Object from PIE level still referenced. Shortest path from root: (Object is not currently rooted)

UE4Editor_Core!FWindowsErrorOutputDevice::Serialize() [d:\build\++ue4\sync\engine\source\runtime\core\private\windows\windowserroroutputdevice.cpp:79]
UE4Editor_Core!FOutputDevice::LogfImpl() [d:\build\++ue4\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:71]
UE4Editor_Core!AssertFailedImplV() [d:\build\++ue4\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:101]
UE4Editor_Core!FDebug::AssertFailed() [d:\build\++ue4\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:449]
UE4Editor_Core!FMsg::LogfImpl() [d:\build\++ue4\sync\engine\source\runtime\core\private\logging\logmacros.cpp:69]
UE4Editor_MessageLog!FMessageLogListingModel::AddMessageInternal() [d:\build\++ue4\sync\engine\source\developer\messagelog\private\model\messageloglistingmodel.cpp:63]
UE4Editor_MessageLog!FMessageLogListingViewModel::AddMessages() [d:\build\++ue4\sync\engine\source\developer\messagelog\private\presentation\messageloglistingviewmodel.cpp:156]
UE4Editor_Core!FMessageLog::Flush() [d:\build\++ue4\sync\engine\source\runtime\core\private\logging\messagelog.cpp:198]
UE4Editor_Core!FMessageLog::~FMessageLog() [d:\build\++ue4\sync\engine\source\runtime\core\private\logging\messagelog.cpp:95]
UE4Editor_UnrealEd!UEditorEngine::EndPlayMap() [d:\build\++ue4\sync\engine\source\editor\unrealed\private\playlevel.cpp:496]
UE4Editor_UnrealEd!UEditorEngine::Tick() [d:\build\++ue4\sync\engine\source\editor\unrealed\private\editorengine.cpp:1888]
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [d:\build\++ue4\sync\engine\source\editor\unrealed\private\unrealedengine.cpp:403]
UE4Editor!FEngineLoop::Tick() [d:\build\++ue4\sync\engine\source\runtime\launch\private\launchengineloop.cpp:3967]
UE4Editor!GuardedMain() [d:\build\++ue4\sync\engine\source\runtime\launch\private\launch.cpp:168]
UE4Editor!GuardedMainWrapper() [d:\build\++ue4\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:145]
UE4Editor!WinMain() [d:\build\++ue4\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:275]
UE4Editor!__scrt_common_main_seh() [d:\agent\_work\3\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
kernel32
ntdll