# Random Cook error appeared 

**URL:** <https://forums.unrealengine.com/t/random-cook-error-appeared/2387601>\
**Category:** Issues and Bug Reporting\
**Tags:** Cooking, fortnite-creative, unreal-editor-for-fortnite, bug-report, editor, fortnite, Cooking-Failed\
**Created:** [March 13, 2025, 2:30am UTC](https://forums.unrealengine.com/t/random-cook-error-appeared/2387601 "2025-03-13T02:30:53Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![DW.Im\_Good.Trust](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@DW.Im\_Good.Trust](https://forums.unrealengine.com/u/DW.Im_Good.Trust)\
**Post date:** [March 13, 2025, 2:30am UTC](https://forums.unrealengine.com/t/random-cook-error-appeared/2387601/1 "2025-03-13T02:30:54Z")

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### Summary

One day I was working on my project as normal, the next day before making any changes I tried to start a session and got a cooking error. Anytime I have tried loading a session since I have gotten the same error. I have tried resaving all my files but it didn’t work. Neither the editor log, or output log have any other errors. The errors in the output log:  
PlatformCook: Error: LogWindows: Error: appError called: Assertion failed: HasAllFlags(RF\_ClassDefaultObject) [File:Z:\UEVFS\Root\Engine\Source\Runtime\Engine\Private\Materials\MaterialInstance.cpp] [Line: 3098]  
Trying to save cooked material instance MID0, missing CachedExpressionData  
PlatformCook: Error: LogWindows: Error: appError called: Assertion failed: HasAllFlags(RF\_ClassDefaultObject) [File:Z:\UEVFS\Root\Engine\Source\Runtime\Engine\Private\Materials\MaterialInstance.cpp] [Line: 3098]  
Trying to save cooked material instance MID0, missing CachedExpressionData

### Please select what you are reporting on:

Unreal Editor for Fortnite

### What Type of Bug are you experiencing?

Other

### Steps to Reproduce

No idea

### Expected Result

Issue listed

### Observed Result

…

### Platform(s)

windows

### Upload an image

 ![Screenshot (320).png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/d/3/1/d31aa9dae9ff1be52248bc6a9d27cd42cc0c3556.png)  
 ![Screenshot (321).png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/9/b/5/9b5bcc61e5e27fa386615ee6927e8c0b3ac52af5.png)

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**Author:** ![DW.Im\_Good.Trust](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@DW.Im\_Good.Trust](https://forums.unrealengine.com/u/DW.Im_Good.Trust)\
**Post date:** [March 13, 2025, 7:16pm UTC](https://forums.unrealengine.com/t/random-cook-error-appeared/2387601/2 "2025-03-13T19:16:25Z")

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This issue was caused by assigning materials to a mesh\_component in a scene graph prefab, clearing the override fixed it

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**Author:** ![Flak](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/flak/32/769441_2.png) [@Flak](https://forums.unrealengine.com/u/Flak)\
**Post date:** [March 13, 2025, 7:20pm UTC](https://forums.unrealengine.com/t/random-cook-error-appeared/2387601/3 "2025-03-13T19:20:36Z")

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Thank you for letting us know! Glad you got it sorted.

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**Author:** ![macxike](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@macxike](https://forums.unrealengine.com/u/macxike)\
**Post date:** [July 18, 2025, 4:05am UTC](https://forums.unrealengine.com/t/random-cook-error-appeared/2387601/4 "2025-07-18T04:05:11Z")

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Hello, I’m suddenly having the same issue after migrating to 5.6. Can you please elaborate on what you mean by “Clearing the override”? Thanks

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**Author:** ![system](https://d3kjluh73b9h9o.cloudfront.net/original/4X/7/1/3/713c9d3f58553f0de89543d76a8a3a2779dc9fa4.png) [@system](https://forums.unrealengine.com/u/system)\
**Post date:** [September 9, 2025, 2:31am UTC](https://forums.unrealengine.com/t/random-cook-error-appeared/2387601/5 "2025-09-09T02:31:20Z")

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