From this UDN: https://answers.unrealengine.com/questions/718928/4180-editor-crash-while-opening-child-blueprint.html
Crash occurs when opening child (or in the repro case, grandchild) blueprints after convert their project to 4.18.
This can still be reproduced in 4.18.1 and latest 4.18.2
RESULT
Crash
Assertion failed: !F->GetSuperFunction() || (F->GetSuperFunction()->FunctionFlags&FUNC_NetFuncFlags) == (F->FunctionFlags&FUNC_NetFuncFlags) [File:D:\Build\++UE4+Release-4.18+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\Class.cpp] [Line: 3068] KERNELBASE.dll!UnknownFunction [] UE4Editor-ApplicationCore.dll!FWindowsErrorOutputDevice::Serialize() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\applicationcore\private\windows\windowserroroutputdevice.cpp:65] UE4Editor-Core.dll!FOutputDevice::Logf__VA() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:70] UE4Editor-Core.dll!FDebug::AssertFailed() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:414] UE4Editor-CoreUObject.dll!UClass::Link() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\class.cpp:3069] UE4Editor-Engine.dll!UBlueprintGeneratedClass::Link() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\blueprintgeneratedclass.cpp:1367] UE4Editor-CoreUObject.dll!UClass::Serialize() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\class.cpp:3531] UE4Editor-Engine.dll!UBlueprintGeneratedClass::Serialize() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\engine\private\blueprintgeneratedclass.cpp:1460] UE4Editor-CoreUObject.dll!FLinkerLoad::Preload() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:3300] UE4Editor-CoreUObject.dll!FLinkerLoad::CreateExport() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:4018] UE4Editor-CoreUObject.dll!FLinkerLoad::IndexToObject() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:4241] UE4Editor-CoreUObject.dll!FLinkerLoad::CreateExport() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:3711] UE4Editor-CoreUObject.dll!FLinkerLoad::IndexToObject() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:4241] UE4Editor-CoreUObject.dll!FLinkerLoad::CreateExport() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:3711] UE4Editor-CoreUObject.dll!FLinkerLoad::CreateExportAndPreload() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:2744] UE4Editor-CoreUObject.dll!FLinkerLoad::LoadAllObjects() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:2902] UE4Editor-CoreUObject.dll!LoadPackageInternal() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:1322] UE4Editor-CoreUObject.dll!LoadPackage() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:1430] UE4Editor-CoreUObject.dll!ResolveName() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:798] UE4Editor-CoreUObject.dll!StaticLoadObjectInternal() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:886] UE4Editor-CoreUObject.dll!StaticLoadObject() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:953] UE4Editor-ContentBrowser.dll!FAssetData::GetAsset() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\assetregistry\public\assetdata.h:283] UE4Editor-ContentBrowser.dll!SContentBrowser::OnAssetsActivated() [d:\build\++ue4+release-4.18+compile\sync\engine\source\editor\contentbrowser\private\scontentbrowser.cpp:1922] UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SContentBrowser,0,TTypeWrapper<void> __cdecl(TArray<FAssetData,FDefaultAllocator> const & __ptr64,enum EAssetTypeActivationMethod::Type)>::Execute() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:327] UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SContentBrowser,0,void __cdecl(TArray<FAssetData,FDefaultAllocator> const & __ptr64,enum EAssetTypeActivationMethod::Type)>::ExecuteIfSafe() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:434] UE4Editor-ContentBrowser.dll!SAssetView::OnListMouseButtonDoubleClick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\editor\contentbrowser\private\sassetview.cpp:3904] UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SAssetView,0,TTypeWrapper<void> __cdecl(TSharedPtr<FAssetViewItem,0>)>::Execute() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:327] UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SAssetView,0,void __cdecl(TSharedPtr<FAssetViewItem,0>)>::ExecuteIfSafe() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:434] UE4Editor-ContentBrowser.dll!TBaseDelegate<void,TSharedPtr<FAssetViewItem,0> >::ExecuteIfBound() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\core\public\delegates\delegatesignatureimpl.inl:624] UE4Editor-ContentBrowser.dll!SListView<TSharedPtr<FAssetViewItem,0> >::Private_OnItemDoubleClicked() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\slate\public\widgets\views\slistview.h:805] UE4Editor-ContentBrowser.dll!STableRow<TSharedPtr<FAssetViewItem,0> >::OnMouseButtonDoubleClick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\slate\public\widgets\views\stablerow.h:288] UE4Editor-Slate.dll!<lambda_eeb33fd1b480e3cad58a1531d90d2e14>::operator()() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5695] UE4Editor-Slate.dll!FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FPointerEvent,<lambda_eeb33fd1b480e3cad58a1531d90d2e14> >() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:234] UE4Editor-Slate.dll!FSlateApplication::RoutePointerDoubleClickEvent() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5693] UE4Editor-Slate.dll!FSlateApplication::ProcessMouseButtonDoubleClickEvent() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5680] UE4Editor-Slate.dll!FSlateApplication::OnMouseDoubleClick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5656] UE4Editor-ApplicationCore.dll!FWindowsApplication::ProcessDeferredMessage() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:1729] UE4Editor-ApplicationCore.dll!FWindowsApplication::DeferMessage() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:2171] UE4Editor-ApplicationCore.dll!FWindowsApplication::ProcessMessage() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:888] UE4Editor-ApplicationCore.dll!FWindowsApplication::AppWndProc() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:725] USER32.dll!UnknownFunction [] USER32.dll!UnknownFunction [] UE4Editor-ApplicationCore.dll!FWindowsPlatformApplicationMisc::PumpMessages() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\applicationcore\private\windows\windowsplatformapplicationmisc.cpp:129] UE4Editor.exe!FEngineLoop::Tick() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\launchengineloop.cpp:3220] UE4Editor.exe!GuardedMain() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\launch.cpp:166] UE4Editor.exe!GuardedMainWrapper() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:134] UE4Editor.exe!WinMain() [d:\build\++ue4+release-4.18+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:210] UE4Editor.exe!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:253] kernel32.dll!UnknownFunction [] ntdll.dll!UnknownFunction [] ntdll.dll!UnknownFunction []
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-52852 in the post.