The issue is relatively simple. XenForo_ControllerPublic_LostPassword::actionLost() line 66: Code: return $this->responseError(new XenForo_Phrase('requested_member_not_found'), 404); This line results in a response code of 404, which the Cloudflare Smart Errors interprets as a regular Page Not Found and replaces the page's contents with a help page. While I can temporarily fix this with custom page rules that disable Smart Errors for this particular page, I am very concerned about how many other pages behave similarly. With Cloudflare's insane popularity I think compatibility with it is essential. My amateur suggestion would be to not ever respond with 404 error codes, because server software and reverse proxies may interpret it in a similar way and lead to some nasty edge cases.