This worked for me:
opening DefaultEngine.ini
and removing the value after “EditorStartupMap=”
Encountered same problem as OP after converting this specific map to WorldPartition earlier,
and closing the Editor and open again after a couple of hours.
Being able to open the project, I could then load the map succesfully.
CrashLog file
[2023.03.25-18.11.06:066][ 0]LogLevelSequenceEditor: LevelSequenceEditor subsystem initialized.
[2023.03.25-18.11.06:092][ 0]LogInit: Display: Engine is initialized. Leaving FEngineLoop::Init()
[2023.03.25-18.11.06:093][ 0]SourceControl: Source control is disabled
[2023.03.25-18.11.06:094][ 0]LogUnrealEdMisc: Loading editor; pre map load, took 8.458
[2023.03.25-18.11.06:094][ 0]LightingResults: New page: Lighting Build
[2023.03.25-18.11.06:099][ 0]LogWorld: UWorld::CleanupWorld for Untitled, bSessionEnded=true, bCleanupResources=true
[2023.03.25-18.11.06:099][ 0]LogSlate: InvalidateAllWidgets triggered. All widgets were invalidated
[2023.03.25-18.11.06:099][ 0]MapCheck: New page: Map Check
[2023.03.25-18.11.06:099][ 0]LightingResults: New page: Lighting Build
[2023.03.25-18.11.06:105][ 0]LogAudio: Display: Audio Device unregistered from world 'None'.
[2023.03.25-18.11.06:108][ 0]LogUObjectHash: Compacting FUObjectHashTables data took 0.61ms
[2023.03.25-18.11.06:325][ 0]LogAudio: Display: Audio Device (ID: 1) registered with world 'Map_Prototyping'.
[2023.03.25-18.11.06:326][ 0]LogEditorServer: Finished looking for orphan Actors (0.000 secs)
[2023.03.25-18.11.06:326][ 0]LogAIModule: Creating AISystem for world Map_Prototyping
[2023.03.25-18.11.06:336][ 0]LogUObjectHash: Compacting FUObjectHashTables data took 0.46ms
[2023.03.25-18.11.06:336][ 0]Cmd: MAP CHECKDEP NOCLEARLOG
[2023.03.25-18.11.06:337][ 0]MapCheck: Map check complete: 0 Error(s), 0 Warning(s), took 0.347ms to complete.
[2023.03.25-18.11.06:337][ 0]LogFileHelpers: Loading map 'Prototyping' took 0.244
[2023.03.25-18.11.06:350][ 0]LogUnrealEdMisc: Total Editor Startup Time, took 8.716
...
[2023.03.25-18.11.06:720][ 0]LogOutputDevice: Warning:
Script Stack (0 frames) :
[2023.03.25-18.11.06:739][ 0]LogWindows: Error: appError called: Assertion failed: WorldPartition->World == World [File:D:\build\++UE5\Sync\Engine\Source\Editor\WorldPartitionEditor\Private\WorldPartition\SWorldPartitionEditor.cpp] [Line: 73]
[2023.03.25-18.11.06:739][ 0]LogWindows: Windows GetLastError: The operation completed successfully. (0)