Which check is NOT related to a security issue?

A page responding with a 5xx code indicates a server-side error, meaning the server failed to fulfill a request. While this impacts user experience and SEO, it's generally not a direct security vulnerability. Mixed content (HTTP resources on an HTTPS page) can expose users to sniffing and active attacks. Using an input type="password" field without HTTPS can lead to credentials being transmitted in plain text, making them vulnerable to interception. Subdomains not supporting secure encryption algorithms (like TLS 1.2 or higher) leave data vulnerable to eavesdropping and tampering. These three issues directly relate to the confidentiality and integrity of data, which are core security concerns.