5.8 (built from source) fails to launch due to .net process stalling

anonymous-edc · June 30, 2026, 9:28pm

Hello,

One of our developers is running into an issue with a built version of 5.8. There seems to be a .net issue where one of the processes that’s spawned is running, but not doing anything. If that process is forced closed, it seems to work.

It seems to launch on other developers machines, but this one is different as it doesn’t have Visual Studio.

I’m attaching a couple of files. One is the project log file. It looks like it’s attempting to launch UBT at one point, which seems weird as this specific machine doesn’t have Visual Studio.

The other is just a screenshot of the list of .net processes and the one that appears to be running, but stalled.

----EDIT----

This problem happens if we just launch UnrealEditor.exe, or if we attempt to open a project. I’ve attached a log from when we’ve tried to open a project. Let me know if that would be helpful to have and I can provi

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step_jac_eg · July 15, 2026, 11:04pm

Hi Karl,

Can you see if you can extract the full command line to dotnet.exe? To do so in the Windows Task Manager, you must enable the “Command line” column within either the Processes or Details tab.

From the Processes Tab (Windows 10 & 11)

Open Task Manager using the shortcut
Ctrl + Shift + Esc
.
Click More details at the bottom if you are in the simple view.
Make sure you are on the Processes tab.
Right-click any existing column header (such as Name, CPU, or Memory).
Hover over or click Command Line to check it.

From the Details Tab (Recommended for exact arguments)

Open Task Manager and navigate to the Details tab on the left menu or top bar.
Right-click on any column header (e.g., PID, Status) and click Select columns.
Scroll down the list, check the box next to Command line, and click OK.
A new column will appear showing the full executable path along with all passed arguments.

Best regards.

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anonymous-edc · July 21, 2026, 5:18pm

dotnet "..\..\Engine\Binaries\DotNET\UnrealBuildTool\UnrealBuildTool.dll" -Mode=ValidatePlatforms -OutputSDKs -AllPlatforms -project="D:/~CYANWORK/Mudfish/Project/MudFish.uproject" -log="D:/~CYANWORK/Mudfish/Project/Saved/Logs/AutoSDKInfo.txt" -verbose -timestamps

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step_jac_eg · August 6, 2026, 3:29pm

Hi Karl,

Is the project in question Blueprint only or has C++ code as well?

Best regards.

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anonymous-edc · August 11, 2026, 4:54pm

It happens when they launch UnrealEditor.exe without a project specified.

It happens when they launch a C++ based project.

And it happens when they launch a blueprint only project.

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step_jac_eg · August 12, 2026, 3:02pm

Hi Karl,

Can you confirm if you see the same behaviour on the machine in question with a default Blueprint template project? If not, it is likely that the project in question may strayed from the default plugin set, causing a need for a valid VS install. Can you provide the UBT log if that is the case?

Best regards.

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anonymous-edc · August 12, 2026, 4:47pm

Hi Stephane,

I’m not sure if I understand the question, but based on what we tested previously, this does happen with a blueprint template project. It does not seem to matter what type of project is used.

In fact, it happens if Unreal Editor is launched without a project. We captured the process information to get the command that the dotnet instance is running under.

52272 dotnet.exe dotnet "..\..\Engine\Binaries\DotNET\UnrealBuildTool\UnrealBuildTool.dll" -Mode=ValidatePlatforms -OutputSDKs -AllPlatforms -log="D:/~CYANWORK/Engine_5.8_Vanilla/Engine/Saved/Logs/AutoSDKInfo.txt" -verbose -timestamps

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anonymous-edc · August 12, 2026, 7:09pm

Here you go! Hopefully that helps!

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step_jac_eg · August 13, 2026, 7:11pm

Hi Karl,

Unfortunately, the log included indicates successful execution and termination. I will try to get my hands on a clean Windows machine and try to reproduce there.

Best regards.

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anonymous-edc · August 20, 2026, 9:46pm

We have just recently ran into this exact issue.

For a new PC/user without Visual Studio, but with a basic setup of Perforce, Epic Games Launcher, UGS and a few .NET runtimes. This is all we have ever needed to get someone up and running with our custom Unreal Editor.

But over the last few days of bringing some new people on with Unreal 5.8.1, syncing with UGS using precompiled binaries, the editor gets stuck on load.

According to the editor log, It gets stuck running one of two commands:

.\Engine\Build\BatchFiles\Build.bat -Mode=ValidatePlatforms -OutputSDKs  -AllPlatforms  -project="D:/DT/Main/Modesto/Modesto.uproject" -log="D:/DT/Main/Modesto/Saved/Logs/AutoSDKInfo.txt" -verbose -timestamps
 
.\Engine\Build\BatchFiles\Build.bat -Mode=QueryTargets -Project="D:/DT/Main/Modesto/Modesto.uproject" -Output="D:/DT/Main/Modesto/Intermediate/TargetInfo.json" -IncludeAllTargets -DontIncludeParentAssembly -DontIncludeProgramTargets

When we run the commands by themselves in a CMD prompt, or if we just run this:

Main\Engine\Build\BatchFiles\BuildUBT.batWe get the following errors trying to build UBT:

D:\DT\Main\Engine\Source\Programs\Shared\EpicGames.Horde\EpicGames.Horde.csproj : error NU1101: Unable to find package BitFaster.Caching. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
D:\DT\Main\Engine\Source\Programs\Shared\EpicGames.IoHash\EpicGames.IoHash.csproj : error NU1101: Unable to find package Blake3. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
D:\DT\Main\Engine\Source\Programs\Shared\EpicGames.MsBuild\EpicGames.MsBuild.csproj : error NU1101: Unable to find package Microsoft.Build. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
D:\DT\Main\Engine\Source\Programs\Shared\EpicGames.Horde\EpicGames.Horde.csproj : error NU1101: Unable to find package Dapper. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
D:\DT\Main\Engine\Source\Programs\Shared\EpicGames.IoHash\EpicGames.IoHash.csproj : error NU1101: Unable to find package JetBrains.Annotations. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
D:\DT\Main\Engine\Source\Programs\Shared\EpicGames.Horde\EpicGames.Horde.csproj : error NU1101: Unable to find package Google.Protobuf. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
D:\DT\Main\Engine\Source\Programs\Shared\EpicGames.IoHash\EpicGames.IoHash.csproj : error NU1101: Unable to find package Microsoft.Extensions.Configuration. No packages exist with this id in source(s): Microsoft Visual Studio Offline Packages
...
and so on until
RunUBT ERROR: UnrealBuildTool failed to compile.

We tried many things to try to get this working. The only thing which finally worked was to run the command:

dotnet nuget add source https://api.nuget.org/v3/index.json -n nuget.orgOf course, that will only work if you have a .NET SDK installed which our non Visual Studios users do not, so we had to install .NET SDK 10 first.

After those 2 things, UBT would build correctly and the editor would run.

So, we have a workaround, but it would be nice for Epic to investigate this and see if they can make sure it works without an extra magical CMD line

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step_jac_eg · August 24, 2026, 5:20pm

Thanks for the additional information. Glad you have a workaround. Surprising you need to install the .NET 10 SDK as it’s included with UE. Clearly, there’s some underlying dependency breaking that on Windows.

Best regards.

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anonymous-edc · September 3, 2026, 5:55pm

Updating this thread as the issue isn’t resolved and shouldn’t be closed.

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anonymous-edc · September 3, 2026, 6:35pm

Our developer attempted to run Build.bat -validateplatforms and it definitely stalls when looking at one of the sdks.

Using bundled DotNet SDK version: 10.0 win-x64
 
UnrealBuildTool is up-to-date
 
Running UnrealBuildTool: dotnet "..\..\Engine\Binaries\DotNET\UnrealBuildTool\UnrealBuildTool.dll" -Mode=ValidatePlatforms -OutputSDKs -AllPlatforms -project="D:\~CYANWORK\Mudfish\Project/MudFish.uproject" -log="D:\~CYANWORK\Mudfish\Project/Saved/Logs/AutoSDKInfo.txt" -verbose -timestamps
 
Log file: D:\~CYANWORK\Mudfish\Project\Saved\Logs\AutoSDKInfo.txt
##PlatformValidate: Win64 INVALID 10.0.22621.0
##PlatformValidate: Mac INVALID 26.1.1
##PlatformValidate: IOS INVALID 26.1.1
##PlatformValidate: Android INVALID r27c
##PlatformValidate: Linux INVALID v26_clang-20.1.8-rockylinux8
##PlatformValidate: LinuxArm64 INVALID v26_clang-20.1.8-rockylinux8
##PlatformValidate: TVOS INVALID 26.1.1
##PlatformValidate: VisionOS INVALID <UNKNOWN>
##PlatformValidate: PS4 INVALID 12.508.031
##PlatformValidate: PS5 INVALID 13.00.00.35
##PlatformValidate: Switch2 INVALID 21.4.2
##PlatformValidate: Switch INVALID 21.4.2
##PlatformValidate: WinGDK INVALID 260400
##PlatformValidate: XB1 INVALID 260400
##PlatformValidate: XSX INVALID 260400
Unable to find required SDK version 'MainVersion' for platform VisionOS. Check your SDK.json files

After cancelling the task, AutoSDKInfo.txt had the temp folder path printed. I’m not sure what it’s supposed to look like, but it appeared to be set to read only. I had them delete it and it came back as read only again after running the command.

Towards the bottom of AutoSDKInfo.txt, after forcing it to cancel, the end of the log had the following.

00:00:00.377] WriteFileIfChanged() wrote 0 changed files of 1 requested writes.
[00:00:00.378] 
[00:00:00.378] Timeline:
[00:00:00.378] [ 0.000] +0.293 Main
[00:00:00.378] 0.033 [ 0.032] +0.123 Apply XmlConfig
[00:00:00.378] 0.163 [ 0.163] +0.041 AddTelemetry
[00:00:00.378] 0.214 [ 0.214] +0.079 RegisterPlatforms
[00:00:00.378] [ 0.299] +0.003 TelemetryService.FlushEvents
[00:00:00.378] [ 0.303]
[00:00:00.378] 
[00:00:00.378] Result: Succeeded
[00:00:00.378] Total execution time: 0.30 seconds

Maybe there’s a write permissions issue?

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step_jac_eg · September 3, 2026, 10:57pm

Hi Karl,

You shouldn’t need to install a .NET SDK. The required version comes prepackaged with UE under %UE_ROOT%/Engine/ThirdParty/DotNet/10.0/win-x64.

Does running:

%UE_ROOT%\Engine\Build\BatchFiles\RunDotnet.bat nuget add source https://api.nuget.org/v3/index.json -n nuget.orgyield a functional setup on machines without installed .NET SDKs?

Best regards.

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anonymous-edc · September 4, 2026, 4:53pm

It did not work for this developer. They get the following message when they run it.

Windows PowerShell
Copyright (C) Microsoft Corporation. All rights reserved.
 
PS D:\~CYANWORK\Engine_5.8_Vanilla> Engine\Build\BatchFiles\RunDotnet.bat nuget add source https://api.nuget.org/v3/index.json -n nuget.org
Using bundled DotNet SDK version: 10.0 win-x64
Running dotnet nuget add source https://api.nuget.org/v3/index.json -n nuget.org
error: The name specified has already been added to the list of available package sources. Provide a unique name.
PS D:\~CYANWORK\Engine_5.8_Vanilla>

However, we might have found a workaround for the issue and it’s unclear as to why it works, but I suspect it’s very much a path related issue.

They had their installation location located at this path.

D:\~CYANWORK\Engine_5.8_VanillaThen, they decided to copy it and try a different location.

D:\~CYANWORK\Engine_5.8_TestAnd the second location seemed to work when launching the engine, but the behaviors reemerged when they launched the project. After launching the project, it affected the editor’s ability to launch with no project specified. So, they changed the location yet again.

D:\Engine_5.8_Vanilla\The third location seems to be working and launching the project just fine.

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step_jac_eg · September 8, 2026, 2:59pm

Interesting, thanks for sharing that finding Karl. It is possible that the ~ in the path is causing an issue downstream. We’ll try to reproduce this under these conditions and confirm the issue.

Best regards.

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step_jac_eg · August 12, 2026, 6:40pm

Hi Karl,

You’ve answered my question, thanks!

Are you able to provide the log file D:/~CYANWORK/Engine_5.8_Vanilla/Engine/Saved/Logs/AutoSDKInfo.txt generated on the offending machine?

Best regards

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