[MAJOR] Some material causes the runnable RHIThread to crash

General Issues and Bug Reporting
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1

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)

2

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.

6

FORT-1041010’s status has changed to ‘Ready for QA’. A member of the QA department is investigating the issue.

7

This issue is really critical. I cannot not assign a material to a mesh in the editor without an RHIThread crash. :frowning:

8

Strange but acceptable workaround for anyone facing it as well:

  • get a list of all material asset names
  • open uefn
  • search for each individual material by its name
  • after going through the list the editor seems not to crash anymore for this particular application session
1 Like
9

Thank you. I’ll pass this info along to see if it helps with the investigation.

1 Like
10

The issue is still present in v39.40 and is very much annoying. The editor keeps crashing so easily. Reopening, recovering lost changes wastes so much of my development time.

11

This is happening to me for one of my materials as well. I don’t know when / how and it only applies to one of my projects right now. If you try to change the material from the drop down menu on an asset the editor closes down and I get the same error you showed. The only way I can get around it right now is to either copy/paste the material from something else that has it already, or finding the material in the content drawer and dragging it onto the material slot like that. Oddly it seems for you that just seeing the material in the content drawer is enough to cause issues in your case. My best guess as to why is that the editor glitches out when trying to create the material thumbnail image, and thus doing something that shows the material thumbnail image will result in the editor closing, at least in sub menus for me.

12

I had this i changed to dx11 and it solves it for me for the most part

1 Like
13

The issue stopped for me, not sure if it was the update or what. If someone else has this issue and can’t find the material that casues it you can try this it worked for me most of the time. SAVE, Then click the material drop down and IMMEDIATLY start typing the name of the mat you want so only that mat shows up. If you get it before the pop-up dialog populates the material previews then it usually is ok.