UEFN unusable, constant crash Assertion failed

Aura SV
Tue, 24 Feb 2026 16:20:23 +0000
Issues and Bug Reporting

Summary

Assertion failed: (::DwmExtendFrameIntoClientArea(HWnd, &Margins)) >= 0 File: WindowsWindow.cpp Line: 359

I’ve formated PC, reverted Driver updates but nothing helped.

I keep getting this crash on UEFN, screen goes black and if i reopen UEFN without restarting PC the whole PC shuts down… If it helps I think it happens mostly when I alt tab or change windows.

I got the logs saved but I don’t know where to send them.

This only happens with UEFN.

RX 6600
Ryzen 5 5600
32gb ram
Windows 11 25H2

Hope someone can help me or that this can be fixed because its impossible to use UEFN like this.

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Stability

Steps to Reproduce

Open UEFN, use it, eventually it will crash. Seems to happen the most when you have Fortnite open and you keep altering between Fortnite and UEFN window.

Expected Result

It shouldn’t crash, you should be able to swap between apps without any problem.

Observed Result

Screen goes black, when it comes back crash report says Assertion failed: (::DwmExtendFrameIntoClientArea(HWnd, &Margins)) >= 0 File: WindowsWindow.cpp Line: 359, then, if I don’t restart my PC, the whole pc will shut down if I reopen UEFN.

Platform(s)

PC

Additional Notes

I saw another person with this issue last month on this forum but he didn’t get any reply.

7 posts - 3 participants