UEFN hangs at 73% Initializing after reinstall; opened successfully once.

General Issues and Bug Reporting
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Summary

UEFN consistently hangs at 73% Initializing on my Windows PC. One attempt remained there for several hours. It occasionally reaches 75%, but usually stops at 73%.

UEFN successfully opened once, and I was able to sync and open my team’s island. After closing it, subsequent launches began hanging again. The issue happens before selecting a project.

Troubleshooting completed:

  • Reinstalled Epic Games Launcher, Fortnite, and UEFN.
  • Confirmed Fortnite launches normally and reaches the lobby.
  • Restarted Windows.
  • Attempted file verification.
  • Tested my home connection and a mobile hotspot, including with the home connection disconnected.
  • Confirmed the launcher’s Use Proxy setting was unchecked.
  • Checked Windows Security and Panda Dome quarantine; neither showed matching detections.
  • Added a Panda Dome firewall rule allowing UEFN outbound TCP/UDP connections.
  • Tested -UDPMESSAGING_TRANSPORT_ENABLE=0 through a shortcut and confirmed the argument appeared in Task Manager. The hang persisted, and UDP initialization still appeared in the log.
    Diagnostic findings:
  • Task Manager’s Analyze wait chain reports multiple UEFN threads waiting to finish network I/O.
  • Recent logs stop advancing around online-services registration and UDP messaging initialization. Later entries show only periodic cache maintenance.
  • No fatal error appears at the end of those logs.
  • Earlier installation attempts produced a missing tbb12.dll error and verification error IS-EO-Ins-NotFnd. Those occurred before the full reinstall; the current symptom is the startup hang.
  • I captured a memory dump while UEFN was hung and can provide it through a secure private upload.
    System: Windows PC, NVIDIA GeForce RTX 4070 Ti SUPER.

I can provide the launcher log and several UEFN startup logs. Please advise on the next diagnostic steps for identifying what is blocking initialization.

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Stability

Steps to Reproduce

  1. Open Epic Games Launcher on Windows.
  2. Launch Unreal Editor for Fortnite from the Library.
  3. Wait for the startup screen to reach 73% Initializing.
  4. Observe that startup remains at 73% and the Project Browser never opens, even after several hours.
  5. End UEFN through Task Manager and relaunch it. The hang occurs again.
    The issue occurs before selecting a project and persists after restarting Windows and reinstalling the launcher, Fortnite, and UEFN.

Expected Result

UEFN should finish initializing and open the Project Browser, allowing me to select, sync, and open my team’s island.

Observed Result

UEFN remains stuck at 73% Initializing and does not open the Project Browser, even after several hours. The process stays running and must be ended through Task Manager. It opened successfully once, but subsequent launches hang again.

Platform(s)

PC — Windows
GPU: NVIDIA GeForce RTX 4070 Ti SUPER