debug kills the browser, I think the output has circular dependencies.
But I know, that item.subItems is an array. If the array is empty, this line is executed and the menu items are rendered. In case that the item has subitems I see this warning and nothing is rendered.
This code fails also with a fresh installed vanilla neos website…
BTW: this notation works:
<f:if condition="{item.subItems}"> …