Log error help.

Hello, I need some help deciphering what some log errors mean. Upgrading a project that is stable at 4.15 to 4.16, it constantly crashes.
The error:

[2017.05.24-23.54.30:292] 0]LogOutputDevice:Error: === Handled ensure: ===
[2017.05.24-23.54.30:292] 0]LogOutputDevice:Error:
[2017.05.24-23.54.30:292] 0]LogOutputDevice:Error: Ensure condition failed: ChildActorTemplate == nullptr [File:D:\Build++UE4+Release-4.16+Compile\Sync\Engine\Source\Runtime\Engine\Private\Components\ChildActorComponent.cpp] [Line: 95]
[2017.05.24-23.54.30:292] 0]LogOutputDevice:Error: Found unexpected ChildActorTemplate LinkerPlaceholderExportObject /Game/FirstPersonBP/Blueprints/ElectricitySystem/Parts/Part_Door.PLACEHOLDER-INST_of_PLACEHOLDER-CLASS__Mod_part_Base_Door_C_5 when ChildActorClass is null
[2017.05.24-23.54.30:292] 0]LogOutputDevice:Error: Stack:
[2017.05.24-23.54.30:292] 0]LogOutputDevice:Error: UE4Editor-Core.dll!0x00000000DFEB32B6

I don’t get what this placeholder-inst is.
So I have this class called Part_Door. It has several child actor components, one of them has the class called “Mod_Part_Base_Door”. And Part_Door is also inside a child actor component of another class, if that helps.
Do I need to provide more information? It’s a pretty complex setup.

The only way I am able to get rid of that error is by deleting the “Mod_Part_Base_Door” class and cleaning up the blueprints that referenced it.

But then I get another error:

[2017.05.25-12.26.32:572] 97]LogOutputDevice:Error: === Handled ensure: ===
[2017.05.25-12.26.32:572] 97]LogOutputDevice:Error:
[2017.05.25-12.26.32:572] 97]LogOutputDevice:Error: Ensure condition failed: !bIsFilteredOut [File:D:\Build++UE4+Release-4.16+Compile\Sync\Engine\Source\Editor\BlueprintGraph\Private\BlueprintActionFilter.cpp] [Line: 1689]
[2017.05.25-12.26.32:572] 97]LogOutputDevice:Error: Invalid BlueprintActionDatabase entry (for SKEL_Part_Door_C). Was the database properly updated when this class was compiled?
[2017.05.25-12.26.32:572] 97]LogOutputDevice:Error: Stack:
[2017.05.25-12.26.32:572] 97]LogOutputDevice:Error: UE4Editor-Core.dll!0x00000000E2D832B6

Now it’s Part_Door, but what the SKEL means I don’t know. I guess I’ll have to try to delete that too?

It’s been a while since I saw skel_ but from what I remember it’s an internal SKELeton class - usually an indication that you’ve found a bug in the engine. If only you could repro it in a clean project, right?

Well. I deleted the Part_Door class, which created the exact same error but for another class. So assuming that would continue, I deleted a bunch of classes, so now all I am left with is the following errors:

LogFeaturePack:Warning: Inserted 1 feature packs
No idea what pack that is or how to fix that.

LogUObjectGlobals:Warning: Failed to find object ‘Class None.’
No idea where that is happening. How am I supposed to find that?


[2017.05.25-13.14.50:819][990]LogThreadingWindows:Error: Runnable thread TaskGraphThreadNP 1 crashed.
[2017.05.25-13.14.50:819][990]LogThreadingWindows:Error: Runnable thread TaskGraphThreadNP 0 crashed.
[2017.05.25-13.14.50:819][990]LogThreadingWindows:Error: Runnable thread TaskGraphThreadNP 2 crashed.

[2017.05.25-13.14.50:819][990]LogWindows:Error: HandleError re-entered.
[2017.05.25-13.14.50:819][990]LogWindows:Error: HandleError re-entered.
[2017.05.25-13.14.50:819][990]LogWindows: FPlatformMisc::RequestExit(1)
[2017.05.25-13.14.50:819][990]LogWindows: FPlatformMisc::RequestExit(1)
[2017.05.25-13.14.50:819][990]LogWindows:Error: === Critical error: ===
[2017.05.25-13.14.50:819][990]LogWindows:Error: Fatal error!
[2017.05.25-13.14.50:819][990]LogWindows:Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0xffffffff
[2017.05.25-13.14.50:819][990]Log file closed, 05/25/17 15:14:50

Okay, I see. I do plan to submit this as a bug report but I am trying to narrow it down as much as possible.

I’m also having the same problem, many classes are getting these “Found unexpected ChildActorTemplate LinkerPlaceholderExportObject” after switching versions to 4.16

So if anyone is curious the errors were because of some child actor components. But as I mentioned, fixing these still caused my project to crash.
I have kind of narrowed it down to one class which, if deleted, fixes it.
On the other hand, deleting 5 other classes also fixes it.

How useful is that information to the bugdepartment? Of course, finding out exactly what is causing a crash, pointing at a specific thing and repro steps is of course the most useful. But making a report, stating “delete this class to fix the problem”, just how useful is that?
Been at this bloody thing for 4 days now.