@Stuart Wright I think this is something to do with your custom menu.
I'm not sure if that's a recent change, that it loads over AJAX? There's code to pass the node_id in, but it never seems to get passed in:
Code:
$.ajax({
url: "{xen:link 'menu/index.json'}",
data: '_xfToken={$visitor.csrf_token_page}<xen:if is="{$node.node_id}">&node_id={$node.node_id}</xen:if>',
The resulting URL is
menu/index.json?_xfToken=<token>
rather than
menu/index.json?_xfToken=<token>&node_id=<node_id>
.