Unreal Crashes attempting to open a level (Assertion failed)

Development Programming & Scripting
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1

Hi, we were working on a scene for a project. The scene was working fine, but after a crash while working on something unrelated, the map couldn’t open anymore. The editor crashes on repeat when trying to open the scene. Here is the error:

Assertion failed: ReaderPos + Num <= ReaderSize [File:D:\build++UE5\Sync\Engine\Source\Runtime\Core\Public\Serialization\BufferReader.h] [Line: 52]

UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_MeshDescription
UnrealEditor_MeshDescription
UnrealEditor_MeshDescription
UnrealEditor_MeshDescription
UnrealEditor_MeshDescription
UnrealEditor_MeshDescription
UnrealEditor_MeshDescription
UnrealEditor_MeshDescription
UnrealEditor_Engine
UnrealEditor_Engine
UnrealEditor_MeshBuilder
UnrealEditor_MeshBuilder
UnrealEditor_Engine
UnrealEditor_Engine
UnrealEditor_Engine
UnrealEditor_Engine
UnrealEditor_Engine
UnrealEditor_Engine
UnrealEditor_Core
UnrealEditor_Engine
UnrealEditor
UnrealEditor
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_Core
kernel32
ntdll

Do you have any idea how to fix this? We do have backup .umap, but they don’t show up when we put them into the Content folder. This is pretty urgent too, so we would rather not have to redo the entire map from scratch…

Feel free to ask for more info if anything’s missing
Thanks in advance

2

Hello,

A couple of questions:

Can you open other projects?
Have you tried verifying/reinstalling Unreal?

3

Hi, thanks for replying. Just to answer, I was able to open this project and other projects just fine. The problem was that opening the scene made the engine crash. However, the issue has been resolved (somehow).

Turns out Unreal saved temporary files, that it is supposed to delete automatically (in this instance, the troublemakers were 5 rocks that couldn’t be removed ; the crash may have stopped the process early).
Removing them fixed the issue entirely. I have no idea why this happened however, and have no idea how to recreate it.

4

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