Summary
Title: Fortnite client hangs on GameThread shortly after joining a UEFN session (Windows Insider build 29683)
Summary:
When I launch a session from UEFN and join on PC, Fortnite hangs a few seconds after spawning (“Hang detected on GameThread”, 45 s heartbeat timeout) and must be force-closed. It happens on every UEFN session I start. It has also happened twice in regular Blitz Royale matches. The same island works fine when I join from PS5.
Please select what you are reporting on:
Fortnite client (when joining a UEFN session)
Platform(s):
Windows PC: MSI Raider 16 HX, Intel Core Ultra 9 275HX, RTX 5070 Ti Laptop GPU (driver 617.42), 32 GB RAM, DirectX 12.
OS: Windows 11 Insider Preview, Dev channel, build 29683.
Additional Notes (crash dump analysis):
The game thread is not waiting on anything. It is spinning at FortniteClient-Win64-Shipping.exe+0xf2b90d8 (42.40). That code walks the base-relocation table of loaded modules. In the dumps it is walking dxgi.dll (10.0.29683.1000).
The walker stops only when a block has VirtualAddress == 0. It does not check the directory size from the data directory. On this Windows build, system DLLs (dxgi.dll, d3d12.dll, kernel32.dll) have a dynamic relocation table directly after the base relocations (it starts 0x00000001, 0x00000050). The walker runs past the real end of the relocation directory and reaches a “block” with VirtualAddress 0x00020002 and SizeOfBlock 0. Because it advances by SizeOfBlock, it never moves forward and loops forever.
Bounding the walk by the data directory’s Size, or treating SizeOfBlock < 8 as the end, would fix it.
I realize Insider builds aren’t officially supported. I’m reporting it because this layout may reach retail Windows later. The first hang happened right after updating to build 29683 on Oct 9; there are no crash reports from before that update. Crash reports with minidumps are available.
What Type of Bug are you experiencing?
Editor
Steps to Reproduce
Steps to Reproduce:
- On Windows 11 Insider Dev build 29683, open any UEFN project and click Launch Session.
- Join the session in the Fortnite client on the same PC.
- Spawn in and walk around for a few seconds.
Expected Result:
The session keeps running normally.
Observed Result:
The game freezes completely. After 45 seconds the hang detector fires and the crash reporter appears. The call stack is identical in all 7 crash reports, on Fortnite 42.30 (CL-58813929) and 42.40 (CL-59343437).
Expected Result
game plays
Observed Result
hang
Affects Versions
5.8
Platform(s)
Windows