The title pretty much explains it all. When creating a blueprint and using a subcomponent or child within that blueprint, deleting the child actor, and then undoing while in play, causes crash.
1. Create a blank Blueprint Project.
2. Create 2 blueprints, BP1 and BP2.
3. Add BP2 as child actor component to BP1
4. Place BP1 into level.
5. Play once, and then stop playing.
6. Delete BP2 child from BP1.
7. Play in Editor again.
8. Without stopping playing return to BP1 editor and hit Ctrl-Z. BP2 subcomponent reappears.
9. Stop playing (crash might occured here as well).
10. Save BP1.
11. Crash
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:258 
UE4Editor_UnrealEd! UEditorEngine::Tick() editor.cpp:1570 
UE4Editor_UnrealEd! UUnrealEdEngine::Tick() unrealedengine.cpp:347 
UE4Editor! FEngineLoop::Tick() launchengineloop.cpp:2257 
UE4Editor! GuardedMain() launch.cpp:142 
UE4Editor! GuardedMainWrapper() launchwindows.cpp:126 
UE4Editor! WinMain() launchwindows.cpp:202 
Head over to the existing Questions & Answers thread and let us know what's up.
| 0 | 
| Component | UE - Gameplay - Blueprint | 
|---|---|
| Affects Versions | 4.7.2 | 
| Target Fix | 4.12 | 
| Created | Mar 12, 2015 | 
|---|---|
| Resolved | May 13, 2016 | 
| Updated | Apr 27, 2018 |