The short answer
A successful result means your browser reached an IPv6-only endpoint and shows the public IPv6 address used for that connection. A missing result does not necessarily mean your internet is broken; IPv4 can continue working separately.
How IPv6 differs from IPv4
IPv6 uses 128-bit addresses, providing vastly more address space than 32-bit IPv4. Its text form uses hexadecimal groups separated by colons, and consecutive groups of zero can be shortened with a double colon.
Many networks operate IPv4 and IPv6 together in dual-stack mode. Your browser chooses a working route for each destination, which is why testing the two families independently gives a clearer result than displaying only the address used to load one page.
Why an IPv6 address can change
Operating systems commonly use temporary IPv6 privacy addresses for outbound connections so one stable interface identifier is not exposed indefinitely. Your provider can also change the delegated network prefix, and a VPN may replace or disable the normal IPv6 route.
A changing address is therefore not automatically a security problem. Firewall policy, software updates and how services are exposed remain more important than whether the hexadecimal address itself stays constant.
Why IPv6 may be unavailable
Your provider, router, mobile access point or VPN may not offer IPv6. It may also be disabled locally or blocked by a family-specific firewall, DNS filter or content blocker. If IPv4 works, ordinary browsing can continue while the IPv6-only check fails.