Check if your VPN leaks your IP address via the WebRTC technology.
23% of tested VPNs leaks users' IPs
Additionally, these STUN requests are made outside of the normal XMLHttpRequest procedure, so they are not visible in the developer console and cannot be blocked by plugins such as AdBlockPlus or Ghostery. This makes these types of requests available for online tracking, de-anonymize and trace users behind common privacy protection services such as: VPN, SOCKS Proxy, HTTP Proxy and (in the past) TOR users.
Read my research on: https://voidsec.com/vpn-leak