[MAJOR] Some material causes the runnable RHIThread to crash

Summary

After v39.20 update, the editor started crashing when I open the project folder where all my materials are present.

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Stability

Steps to Reproduce

  • Open my project
  • Open the VZMaterials folder and wait a few seconds
  • Filtering the content folder by material type produces the same crash

Expected Result

Editor should not crash.

Observed Result

[2026.01.14-07.32.58:673][326]LogThreadingWindows: Error: Runnable thread RHIThread crashed.
[2026.01.14-07.32.58:722][326]LogWindows: Error: === Critical error: ===
[2026.01.14-07.32.58:722][326]LogWindows: Error: 
[2026.01.14-07.32.58:722][326]LogWindows: Error: Fatal error!
[2026.01.14-07.32.58:722][326]LogWindows: Error: 
[2026.01.14-07.32.58:722][326]LogWindows: Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION 0x0000000000040000
[2026.01.14-07.32.58:722][326]LogWindows: Error: 
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x0000000000040000 UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdb5c972c6 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdb5c7a394 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdb5c851df UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdb5c9772d UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdb5c8f030 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdadf02014 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdadf150bf UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdadf0271e UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdacbfb50b UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdabd729b4 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdabd6bd61 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdade37fae UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdac019ae7 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffdac019009 UnrealEditorFortnite-Engine-Win64-Shipping.dll!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: [Callstack] 0x00007ffe52567374 KERNEL32.DLL!UnknownFunction []
[2026.01.14-07.32.58:722][326]LogWindows: Error: 
[2026.01.14-07.32.58:722][326]LogWindows: Error: Crash in runnable thread RHIThread

Platform(s)

PC (UEFN v39.20)

Island Code

2892-4984-5194

Additional Notes

If you can access my project via the above public island code then you can reproduce the issue with v39.20 editor all the time. If you need crash logs, please dm me and I’ll send them in private.

Graphics Driver is updated to the latest available version: 591.74 (NVidia GeForce 3080 TI)

I ruled out material functions (mf_) and can confirm that materials and material instances (m_ and mi_) search queries reproduce the crash. I’m trying to nail down which material it is.

FORT-1041010 has been added to our ‘To Do’ list. Someone’s been assigned this task.