A bug was reported by nathank where 3rd-level category nesting (enabled via SiteSetting.max_category_nesting = 3) interacts poorly with the Header Categories Navbar theme component, causing page load failures and console errors when navigating to sub-sub-categories — though pages load correctly when opened in a new tab. Disabling the theme component resolves the issue, but nathank notes reliance on it. sam escalated the issue to Kris, and awesomerobot confirmed the fix via a pull request, which adjusts the component to support the extra nesting level. The issue highlights a compatibility gap between advanced category structures and the theme component, now resolved.
(this doesn’t appear when in categories or sub-categories)
Workaround / other issues
The sub-sub-category page actually loads okay if opened in a new tab/window, but there are glitches in the navbar functionality and this similar error in the console: