I’ve tracked a bug that’s been popping up for me since I started with UE 5.6 where an Unreal Editor project will simply no longer display after many successful startups.
Turns out that using a multi monitor setup causes your project to store screen locations (so it seems) then in some scenarios (like unplugging monitors) causes that project to refuse to be displayed upon future restarts of Unreal Editor.
The issue was that each project stores its own editor window configuration in ProjectFolder/Saved/Config/MacEditor, and those configs had my windows positioned on displays that no longer exist.
To prevent this you must always quit Unreal Engine properly before unplugging monitors
Or, if you forget and it happens again run:
rm -rf "/path/to/YourProject/Saved/Config/MacEditor/"
UPDATE - CRASH AFTERWARD
I’ve noticed that refocusing UE after bluring, say to my browser or other app, returning to focus UE is super-wonk. That being said I’m seeing crashes per FMacWindow all this together may warrant a legit user story to improve/rethink MacOS window handling.
The crash occurred in FMacWindow::ApplySizeAndModeChanges() - this function handles window resizing, moving, or changing display modes (like switching between windowed/fullscreen).
Key Observations
-
Window became main focus - The stack trace shows
windowDidBecomeMain:which means the crash happened when a window was gaining focus/becoming active -
Run loop processing - It was processing events on the main thread through the Cocoa run loop
-
Signal caught - Something went wrong during the window size/mode application, causing a signal (likely SIGSEGV or similar)
I am on a Macbook Pro, MacOS 26.1, M2 Max / 32gb ram, UE 5.7
Laptop screen plus two monitors