A VPN can handle regular browser traffic while other requests still leave through your normal connection. WebRTC, DNS lookups, and IPv6 traffic each use different routes, so one of them may reveal network information even when the VPN appears to be working. You can read about what an IP leak is here https://gologin.com/blog/what-is-an-ip-leak/ . If WebRTC exposes your address, change its privacy settings or use a browser that controls those requests properly. If the leak comes from DNS or IPv6, make sure your VPN supports and routes that traffic instead of relying only on an extension. Run the same test again after every browser or VPN update, since a changed setting can reopen the leak.