TRY 31.00 first as this may be fixed see post below
This is another look at this and now have some text to look at but not much use afraid
You have corrupted an asset, which is similar to the problem below.
Looks like you turned on Landscape World streaming which is supported in
ue5.5 standard Engine.
UEFN Landscape mode in UEFN 5 version is covered in UEFN documentation
Taken from documentation link below
1 Create New Creates a new Landscape in your Level.
Landscape Mode | Unreal Editor for Fortnite Documentation
ue5 standard Engine see the posting
Landscape streaming proxies loads in too late when PIEing with world partition
The video is for ue5 standard engine NOT UEFN
Getting Started with UE5 World Partitioning for Landscapes (youtube.com)
In this picture “Enable Streaming” has been ticked and this is not supported in UEFN
Your project now has an unsupported function.
This is the same problem as activating a broken plugin, which does not show until you restart you project which fails.
The problem with UEFN is its NOT controlled in the startup file ProjectName.uproject.
Rather obviously this is UEFN is ProjectName.uefnproject because it not the same format
There is little knowledge of UEFN control files and how to turn this off manually
The crash lines in UE5 source code comments talks about putting out an error message above which means that World Partition streaming has been enabled incorrectly.
My other idea is to install UEFN on another PC and download on another PC using Unreal Revision Control.
Check that the project runs on the newly installed PC
Transfer get a clean USB and transfer/copy the project to USB.
Check that the project runs on the newly installed PC again
Compare all the .ini files to see which have changed,
Maybe DefaultEngine.ini
[/Script/WorldPartitionEditor.WorldPartitionEditorSettings]
CommandletClass=Class'/Script/UnrealEd.WorldPartitionConvertCommandlet'
has something else in this area
UEFN C:\Program Files\Epic Games\Fortnite\Engine\Config\BaseEngine.ini
contains
[/Script/Engine.WorldPartitionSettings]
EditorHashDefaultClass=/Script/CoreUObject.Class'/Script/Engine.WorldPartitionEditorSpatialHash'
RuntimeHashDefaultClass=/Script/CoreUObject.Class'/Script/Engine.WorldPartitionRuntimeHashSet'
So if there is anything else remove extra lines especially if its to do with streaming
Try copying the ProjectName.map in place of the original to see if this will work.
Good Luck
The thing to do is save frequently using Revision control