Cooking Error "Content is missing from cook. Source package referenced an object in target package but the object was stripped out of the target package when saved."

Development Programming & Scripting
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This is a follow up to this thread: [Intermittent Cook Error "object was stripped out of the target package when [Content removed]

I’ll recap the essentials:

  • We sometimes get the error “Content is missing from cook. Source package referenced an object in target package but the object was stripped out of the target package when saved.” while cooking our game.
  • It started with UE 5.5.3, some time end of May, several months into us using said engine version.
  • We updated to 5.6.0 in the meanwhile, still getting the error.
  • Simply rerunning the build usually “fixes” it, letting the cook finish. Sometimes multiple cooks in a row fail, but (almost) never with the same assets affected.
  • Occurrence is highly random. Sometimes 20 builds in a row work fine, then the next 3 have the error, then the next 5 work fine again.
  • Happens on all our build agents as well as on local cooks.
  • The source package mentioned in the error is always a “_Generated_” package from some level.
  • The target is always a child blueprint in a blueprint hierarchy.
  • The referenced object is always something inherited from the parent.
  • It seems like when it happens, all instances of the blueprint in that level error out.

Here’s an example of such an error from one of our cooks:

01:54:27 LogCook: Error: Content is missing from cook. Source package referenced an object in target package but the object was stripped out of the target package when saved. 01:54:27 Source package: /Game/GG/Levels/Atlantis/WP_Atlantis/_Generated_/47WZYRHL2HSDOVKRK0OC4RPQZ 01:54:27 Target package: /Game/GG/Props/SimpleInteractables/BP_Candle_01_Interactable 01:54:27 Referenced object: /Game/GG/Props/SimpleInteractables/BP_Candle_01_Interactable.BP_Candle_01_Interactable_C:SM_CandleFlame_Base_GEN_VARIABLEWe also have something new to report:

We were so annoyed by this error regularly popping up and torpedoing even our local test builds, that we tried “the stupid thing” and simply ignored it, continuing the cook.

The assumption was that some asset or component would then be missing from the cooked build, but so far it seems that everything behaves completely normal - in one cook it complained about a very specific mesh component, and upon checking the mesh component seems to be in the final build. So potentially this is a false positive?

Mentioning [mention removed]​ here :slight_smile:

Ciao, Daniel!

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Hi Daniel,

Just to help us track this down, what UE version did you use prior to 5.5.3? Also, is the referenced object always the same component type?

Thanks,

Dave

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Hi!

The complete provenience of the project is:

  • Started with UE 5.1.1 on May 30th 2023
  • 5.2.1 on August 25th 2023
  • 5.3.2 on December 14th 2023
  • 5.4.2 on July 15th 2024
  • 5.5.3 on February 7th 2025
  • 5.6.0 on July 2nd 2025

As far as I was able to see from the logs, all components that were affected were static mesh components (either UStaticMeshComponent, or a simple derived class we use which adds gameplay tags to it).

Ciao, Daniel!

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Thanks for the info.

> It started with UE 5.5.3, some time end of May, several months into us using said engine version.

If didn’t start until several months into using 5.5.3, do you know if this was only affecting new content made in this engine version? If it affected older content, was the content resaved in 5.5.3?

Could you give me an idea of what the most trivial actor affected by this might look like? For example, is this something that could be recreated on my end with a trivial actor + static mesh component in a world partition level?

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Hi!

| If didn’t start until several months into using 5.5.3, do you know if this was only affecting new content made in this engine version? If it affected older content, was the content resaved in 5.5.3?

It does affect blueprints created before 5.5.3 as well as ones freshly created with 5.5.3. However I was not able to find a single incident where the affected object was not either created or resaved in 5.5.3.

This may be coincidence, since most blueprints were touched since we rolled out 5.5.3.

| Could you give me an idea of what the most trivial actor affected by this might look like? For example, is this something that could be recreated on my end with a trivial actor + static mesh component in a world partition level?

AFAICT this only effects instances of blueprints that come from a hierarchy. It exclusively affects static mesh components that are inherited from a parent. I’ve never seen a child-added static mesh component be affected.

As such, the objects usually are at least in some form non-trivial - usually something interactable, like a chest you can open, candle you can turn on/off, a fridge that can be opened, a dispenser with a button, a wobbly platform that collapses when stood upon, etc…

That last example is also the most trivial one I could find. Screenshot is attached, as explanation:

  • BP_CollapsingPlatform03_NoRespawn is exactly what it sounds like - a rickety platform that you can hop on, it wobbles for a bit, then disintegrates. It doesn’t respawn once it has collapsed.
  • Its parent is BP_CollapsingPlatform03 which is exactly the same, only it does reset after a few seconds.
  • All components on it are inherited.
  • The root C++ type is APL_ActorWithAbilitySystem, which inherits from AActor plus IAbilitySystemInterface plus IGameplayTagAssetInterface, and adds a default UPL_AbilitySystemComponent.
    • DefaultSceneRoot and the Platform static mesh underneath it are standard Unreal components
    • I doubt the other three components have anything to do with the issue. They are on all of the affected objects - however they are on almost all of our non-trivial blueprinted and inherited actors, so the overlap here is likely coincidental. They also don’t do anything that should have any influence on the cooking process.

If you peel away the three components at the bottom, what remains is a parent actor blueprint with a static mesh component, and a child blueprint actor that doesn’t have a single property of the parent changed.

[Image Removed]I’m currently trying to see if we can somehow give you either the entire project or at least a part of it. Considering there is third party intellectual property involved (it’s a licensed game), I’m not too optimistic however.

Ciao, Daniel!

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Unfortunately, I’ve not been able to repro this on my end in 5.6 after trying several variations.

Is there any way that you could isolate the problem in a minimal stand-alone project with proprietary content removed?