# UEFN cook\_failure since latest update – Array index out of bounds during cook 

**URL:** <https://forums.unrealengine.com/t/uefn-cook-failure-since-latest-update-array-index-out-of-bounds-during-cook/2728812>\
**Category:** Issues and Bug Reporting\
**Tags:** unreal-engine, unreal-editor-for-fortnite, question, fortnite\
**Created:** [June 15, 2026, 2:56pm UTC](https://forums.unrealengine.com/t/uefn-cook-failure-since-latest-update-array-index-out-of-bounds-during-cook/2728812 "2026-06-15T14:56:37Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![CODEHOANI](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@CODEHOANI](https://forums.unrealengine.com/u/CODEHOANI)\
**Post date:** [June 15, 2026, 2:56pm UTC](https://forums.unrealengine.com/t/uefn-cook-failure-since-latest-update-array-index-out-of-bounds-during-cook/2728812/1 "2026-06-15T14:56:38Z")

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### Summary

Hello,

Since the latest Fortnite / UEFN update, my project no longer cooks or launches correctly.  
Before the update, the project was working, but now I get a cook failure when trying

I already tried creating another almost empty level / removing content, but the cook error still happens, so I’m not sure if the issue is coming from a corrupted actor, runtime data layers, or something introduced by the latest update.

### Please select what you are reporting on:

Creative

### What Type of Bug are you experiencing?

Live Edit

### Steps to Reproduce

launch session

### Expected Result

run the session

### Observed Result

PlatformCook: Error: Nous avons subi une erreur en préparant ce contenu.  
PlatformCook: Error: cook\_failure  
LogWindows: Error: appError called: Assertion failed:  
(Index \>= 0) & (Index \< ArrayNum)  
[File: Z:\UEVFS\Root\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 1339]  
Array index out of bounds: 15 into an array of size 14

### Platform(s)

pc

### Island Code

7563-7108-6934

### Upload an image

![bug1.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/4/a/a/4aaa9676ab54399141c7c6b74b43b749ce17f744.png)

 ![BUG2.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/d/5/a/d5a453e58aa6745c864fa7887053f4c7bbe81282.png)

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<div class="post-metadata">

**Author:** ![Jimbohalo10](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/jimbohalo10/32/961440_2.png) [@Jimbohalo10](https://forums.unrealengine.com/u/Jimbohalo10)\
**Post date:** [June 15, 2026, 6:36pm UTC](https://forums.unrealengine.com/t/uefn-cook-failure-since-latest-update-array-index-out-of-bounds-during-cook/2728812/2 "2026-06-15T18:36:04Z")

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hi @CODEHOANI

From the log looks like your installation try to

[Verify UEFN](https://forums.unrealengine.com/t/urc-exe-and-urc-dll-get-flagged-as-malware-from-microsoft-defender/1802519/5)

If this does not work you need to uninstall UEFN and re-install because you are missing major parts of UEFN

![BUG2NeedVerify](https://d3kjluh73b9h9o.cloudfront.net/original/4X/0/4/0/040cf426dd37e1741b5da0febbcfb7c208843dd7.png)