[5.0.2] “Unexpectedly encountered placeholder class while serializing a component” Crash after migrating from 4.26.2 to 5.02

Everything was working fine in my main project in UE 4.26.2
I selected some assets and migrated them and all their references to another UE 4.26.2 project (copied configutation settings, plugins and Unreal Project File)
Everything was working fine
Then I created another project, this time I switched to UE 5.02
I recompiled plugins earlier and copied them to the project directory
Then I migrated assets and opened project
And at 95% when level is supposed to open…

KA-BOOM!

[2023.03.20-22.21.37:464][ 0]LogOutputDevice: Warning:

Script Stack (0 frames):

[2023.03.20-22.21.37:820][ 0]LogStats: FPlatformStackWalk::StackWalkAndDump - 0.356 s
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: === Handled ensure: ===
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error:
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: Ensure condition failed: false [File:D:\build++UE5\Sync\Engine\Source\Runtime\Engine\Private\Components\ChildActorComponent.cpp] [Line: 122]
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: Unexpectedly encountered placeholder class while serializing a component
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: Stack:
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff929a45ad5 UnrealEditor-Engine.dll!UnknownFunction []
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99ebb6 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a950eb7 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a993cad UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab59147 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:820][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a76e243 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99efb9 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a95099a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a94eac2 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a94f4f4 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a950e5b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a993cad UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab59147 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a76e243 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99efb9 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a95099a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a950e5b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a993cad UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab59147 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a76e243 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99efb9 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a95099a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a950e5b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a993cad UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab59147 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab57b7a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab580d0 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab7bfa4 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab7b6d5 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93aa8140e UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93aa93a34 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93aa8f5ae UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93aa8f44f UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93aa8e483 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a708b5b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff92732a419 UnrealEditor-UnrealEd.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff927329c13 UnrealEditor-UnrealEd.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff9278fa916 UnrealEditor-UnrealEd.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff92b10a955 UnrealEditor-Engine.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff92b59802b UnrealEditor-Engine.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99ebb6 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff92b0ff42a UnrealEditor-Engine.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93aa94b09 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93aa9e0e5 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a90f94a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a90969b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a908ebe UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99ebb6 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a8bf653 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a8bcbae UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff9298cd566 UnrealEditor-Engine.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a90882b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff9298e08ef UnrealEditor-Engine.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99ebb6 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a95099a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a94f4f4 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a950e5b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a993cad UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab59147 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a93bad4 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f45f0 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f2c27 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f469f UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f2c27 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a952648 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a76f8c6 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a76e290 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99efb9 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a95099a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a950e5b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a993cad UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab59147 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a93bad4 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f45f0 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f2c27 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f469f UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f2c27 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a952648 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a76f8c6 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a76e290 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a99efb9 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a95099a UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a950e5b UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:821][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a993cad UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93ab59147 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a93bad4 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f45f0 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f2c27 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f469f UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f2c27 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9f2673 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9683bf UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a9ed40c UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a952e71 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error: [Callstack] 0x00007ff93a983aa9 UnrealEditor-CoreUObject.dll!UnknownFunction []
[2023.03.20-22.21.37:822][ 0]LogOutputDevice: Error:
[2023.03.20-22.21.37:831][ 0]LogStats: SubmitErrorReport - 0.000 s

But probable cause was the Blueprint Actor Child naming
There is one Parent Actor and two Children
obraz
In 4.26.2 it wasn’t a problem
But in 5.02 it is cause of the crash as far as I know
When I renamed Children as below editor stopped crashing at startup and I can select and open every asset in project it does not matter if it has errors
obraz

Without Startup Map, Editor is opening without crash…no its not level fault…when I select above assets (before renaming) in content browser after loading without map editor crashes
I was deleting every folder from project Content folder,one by one, and I was putting them back to the point I found out the culprint…
I know about incompatibility between these versions , some of them okay … I need to convert Double to Single Float Values in some Widgets, find and replace functions if they are missing, etc…but this Crash was like face punch

Now I am going to fix everything related to differences between 4.26.2 and 5.02
And I will try to package the project
I will update this post if something change, I hope not…

EDIT:
So as I thought wrong naming of Parent Chilren wasn’t wrong at all !
I was so excited that I opened the project without crash with all assets migrated that I forgot it all worked because of broken references.
I renamed two children in Windows Explorer and then renamed them again inside Editor.
When I fixed all errors and relaunched project editor crashed again.

So I started to search more about those Character actors and related components and found out this:

Because they use components from this system i checked that

I needed to delete Children only so Character-AI and Character-Player
obraz
For some reason Character-Base was not the cause of the crash
It was good to me because this meant skipping fixing all actor Character-Base references (I deleted only Children , so moving them back will break references related to them only)

I moved Components folder somewhere else
Everything saved correctly i clicked Fix Up Redirectors in the Folder, too

Character-AI had no refferences and Character-Player had two
I fixed errors and restarted project few times after to be sure
and it worked!

I will update this post if editor will start crashing again for some reason

EDIT 2:
I moved Components folder while in 4.26.2 project then migrated to 5.02 and no changes are required. Crashes are gone!