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Assertion failed - WorldPartition error on startup

Put simply - I’ve been working on a new UE5 project with WorldPartition, and all of a sudden whenever I load the editor it crashes with the following trace. I’ve tried removing temporary / intermediate folders, rebuilding project from source - to no avail. At the moment my project is unavailable because of this error (at startup). Any ideas appreciated.


Assertion failed: !StreamingPolicy [File:D:/build/++UE5/Sync/Engine/Source/Runtime/Engine/Private/WorldPartition/WorldPartition.cpp] [Line: 305]

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I’m getting a similar error. I also deleted the intermediate and saved folder but nothing…

Hi @Sheprekt, @halerooks,
I have looked into the World Partition source code for the UE5EA Engine, the failure line is in the middle of Editor World Partitioner, this has nothing to do with initialising the streaming.

I believe that commenting out this line will have no harm to the UE Editor. I have tried it on my UE50EA vs2022 repository, which will run on VS2019 only if you need to.
see Visual Studio 2022 Preview is 64 bit and compiles and runs UE 5.0 EA approximately 20% FASTER - Development Discussion / Unreal Engine 5 Early Access - Unreal Engine Forums

If this patch works tell me and I will submit an official bug report.

having the same issue trying to open one of my maps

I’ve had this and managed to fix it, but it’s frustrating.

If it’s crashing because the default level is the problem, and you don’t care about that level, you can open your project in a file browser, and just swap the name of the problematic level with another level. They are usually in the Levels directory in your project’s files and will have a .umap file extension.

If you want to try to restore the broken level, it isn’t pretty, but I’ve worked around this by, again, opening the project in a file explorer. You would need to have autosave enabled before the crash. This wouldn’t work if you’ve disabled autosave.

There’s a World Partition directory in your project’s files, and opening this up, there’s a directory with a huge number of other directories all with two-letter names like 5Y or 4C or BJ.

One of these is causing the problem. I don’t know any way to find out which one, but if you start by moving half of these directories to a temporary place elsewhere on your computer, and try starting the engine, you can narrow it down.

If you moved half of them and it still crashes, move that half back and try temporarily moving the other half.

Once you know which half is the problem, take half of THOSE files and move them, basically a process of elimination.

This isn’t perfect, because you will lose some of your level depending what was in the removed directory, and it takes forever, but it will get you up and running again with enough patience.

This is probably caused by a null reference, so something like, if your World Partition data relies on being able to find a specific thing, like a material (maybe?) and it can’t, it handles this very badly and crashes. It seems likely to be caused by doing a force delete, or an engine crash in the middle of a regular (but perhaps large) delete, but I can’t rule out other causes.

Easiest way to avoid this problem is not to enable World Partition, but that’s quite extreme.

Another way would be to avoid doing anything that requires a force delete, until you’re happy with your project. Then back up the entire project, do all your force deletes at once, and you can just restore the entire project if you trigger this error.

Hopefully someone with more knowledge can add more or better ways to this thread, until the engine is updated to better handle these situations.

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We’ve started working with World Partitions as well, it is bleeding edge technology so bugs are expected. From our experience it happens if you delete a uasset from the content folder, but not from the level. This is an issue with the One File Per Actor feature.

These One File Per Actor files, kind of work like redirect files, so if you delete an asset from content folder but not the level this pseudo redirect file can’t find it’s source and crashes.

Hopefully you use Git or Perforce or some type of version control system. Or at least keep a backup copy from the day before. :grinning:

Easiest way to solve this is to navigate to your project folder into Saves/Logs . Open your log file after the crash, scroll all the way to the bottom. There you will see a stack track, scroll just above the stack track and look for the error(s). You will see something like:

/Game/SomeFolder/Environment/Walls/BP_Wall_Big_01 : Failed to load ‘/Game/SomeFolder/Environment/Walls/BP_Wall_Big_01’: Can’t find file. /Game/SomeFolder/Environment/Walls/BP_Wall_Big_01

You will need to restore that file(s). Then your map will load. Just be sure when you delete from the Content Folder, delete it from your maps first.

A side note, looks like One File Per Actor doesn’t show as referenced in the World Partition level, so you will not get any warning when you delete content.

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Also having the same issue and tried everything…