Server Travel from Map A to Map B then back to Map A will crash on exiting PIE

Server Travel from Map A to Map B then back to Map A will crash on exiting PIE.

Generates different call stacks between 4.8.1 and Main.

Crash Reporter:
4.8.1: [Link Removed]
Main: [Link Removed]

Call Stack from 4.8.1:
Fatal error: [Link Removed] [Line: 70] Critical Error Package /Game/Maps/MapA Object from PIE level still referenced. Shortest path from root: (Object is not currently rooted)

UE4Editor_MessageLog!FMessageLogListingModel::AddMessageInternal() messageloglistingmodel.cpp:70
UE4Editor_MessageLog!FMessageLogListingModel::AddMessages() messageloglistingmodel.cpp:89
UE4Editor_Core!FMessageLog::Flush() messagelog.cpp:188
UE4Editor_Core!FMessageLog::~FMessageLog() messagelog.cpp:91
UE4Editor_UnrealEd!UEditorEngine::EndPlayMap() playlevel.cpp:289
UE4Editor_UnrealEd!UEditorEngine::Tick() editorengine.cpp:973
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() unrealedengine.cpp:366
UE4Editor!FEngineLoop::Tick() launchengineloop.cpp:2359
UE4Editor!GuardedMain() launch.cpp:142
UE4Editor!GuardedMainWrapper() launchwindows.cpp:126
UE4Editor!WinMain() launchwindows.cpp:200

Call Stack from Main:
Fatal error: [Link Removed] [Line: 633] Unknown token

UE4Editor_CoreUObject!FReferenceChainSearch::ProcessObject() referencechainsearch.cpp:635
UE4Editor_CoreUObject!FReferenceChainSearch::PerformSearch() referencechainsearch.cpp:384
UE4Editor_CoreUObject!FReferenceChainSearch::FReferenceChainSearch() referencechainsearch.cpp:647
UE4Editor_CoreUObject!StaticExec() obj.cpp:3191
UE4Editor_UnrealEd!UEditorEngine::EndPlayMap() playlevel.cpp:269
UE4Editor_UnrealEd!UEditorEngine::Tick() editorengine.cpp:978
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() unrealedengine.cpp:364
UE4Editor!FEngineLoop::Tick() launchengineloop.cpp:2396
UE4Editor!GuardedMain() launch.cpp:142
UE4Editor!GuardedMainWrapper() launchwindows.cpp:126
UE4Editor!WinMain() launchwindows.cpp:200

Reproduced in 4.8.1 and Main (//depot/UE4/Promoted-CL-2605171). This is a regression: did not occur in 4.7.6

1. Open any project
2. Create two new maps
3. PIE
4. Server Travel from Map1 to Map2
5. Server Travel from Map2 to Map1
6. Stop PIE

Result:
Crash