Summary
Creating MVVM ViewBindings inside a Modal Dialog Variant (especially Button event bindings for the Pop-up Dialog Device) consistently causes a cook failure when launching in-editor.
After the cook failure, UEFN crashes when reloading the widget, and the widget becomes permanently corrupted and cannot be reopened nor reloaded.
Please select what you are reporting on:
Unreal Editor for Fortnite
What Type of Bug are you experiencing?
Assets
Steps to Reproduce
Create a new Modal Dialog Variant Widget Blueprint in UEFN.
Start adding ViewBindings to buttons with the CreativeModalDialogViewmodels and add Events such as OnClicked/OnHovered/OnUnhovered (Button Events were the most common trigger).
At some point during binding, deleting & keeping a few bindings empty, the following message appears in the output log:
Ensure condition failed: false â MVVMBlueprintViewEvent⌠was created in invalid Outer /Script/CoreUObject.Package
Save the widget and attempt to launch in (âStart Sessionâ).
The launch fails with a Cook Failure.
Close and restart UEFN.
Try to open or reload the affected widget.
UEFN crashes immediately. The widget is now permanently corrupted:
⢠cannot open
⢠cannot reload
⢠cannot validate
⢠duplicating still crashes
Expected Result
The Widget Blueprint with ViewModel/ViewBindings should launch normally after cooking, and should reopen without crashing after restarting UEFN.
Observed Result
⢠Cook Failure during launch
⢠After restart, opening or reloading the UserWidget instantly crashes UEFN
⢠The widget becomes unrecoverable and breaks the project state
⢠Crash reporter shows:
EXCEPTION_ACCESS_VIOLATION
and
Ensure condition failed: false â MVVMBlueprintViewEvent_0 ⌠created in invalid Outer /Script/CoreUObject.Package
Platform(s)
PC â Windows 11
UEFN Latest Public Version
Additional Notes
⢠The corruption only occurs after ViewBindings are created.
⢠Duplicating the widget before adding bindings works fine.
⢠After adding bindings and triggering the MVVM error message, the next cook attempt breaks the asset permanently.
⢠Rebuilding the widget from scratch reproduces the same failure as soon as MVVM bindings are added (And the error message appears)
