When attempting to use Toolbar(id: "") this crash occurs immediately upon showing the window. FAULT: NSInternalInconsistencyException: NSToolbarItemViewer's min/max size is nan. This indicates an item's size has been changed during layout which is illegal; { NSAssertFile = "NSToolbarItemViewer.m"; NSAssertLine = 942; } If I comment out the toolbars, re-run show the window once, then re-add id: the window properly displays, allows customization and does not error unless I clear data within ~/Library/Containers.