What does this warning mean? In my main app, whenever this warning is logged, the outline view begins to behave weirdly after that, overlapping rows and not responding to clicks anymore. When not using automatic row heights or group rows, the warning doesn't appear anymore. A sample project can be found here.
An interesting thing is that even if there are no group rows, simply implementing the data source method
func outlineView(_ outlineView: NSOutlineView, isGroupItem item: Any) -> Bool {
return false
}
makes the warning appear.