Strange log message and node not found for anonymous
Check your custom 404 configuration at admin/config/system/site-information.

Also check if this custom configuration is directing users to a Panels page (check Structure &gt; Panels or Structure &gt; Pages if you have Panels and Page Manager installed). They may be handling different custom 404 pages for different roles. Perhaps the Panel variant that handles the 404 page for anonymous is missing or redirecting to a non-existing page.