Created attachment 164785 [details]
Basic QML file showing how to reproduce the crash in pure Qt. Not sure if this is a bug in Qt or a misuse of Templates.

SUMMARY
When the OverlayDrawer is visible and modal is changed from true to false, the app crashes. The crash can be fixed by inheriting from QtQuick.Controls.Drawer instead of QtQuick.Templates.Drawer. I'm not sure if this is a bug in Qt Quick or if Kirigami is misusing the template, hence why I'm reporting the bug here.

I've attached a minimal Qt-only demonstrating the issue. Run the code and press the button twice and the app will crash. Swap T.Drawer for C.Drawer and the app works just fine.

In terms of apps the issue can be reproduced in Koko:
1. Run app in desktop mode
2. Reduce the window width until the sidebar hides and becomes modal
3. Increase the window width

Observed result: app crashes
Expected result: non-modal sidebar re-appears

Can also be reproduced with the Sidebar.qml example provided by Kirigami.