question: How to resolve connection issues or error messages on Android
answer: 
  This guide shows you how to resolve connection issues or error messages that are specific to the ExpressVPN Android app. For general connection issues, refer to other troubleshooting guides.
  
  Which connection issue or error message are you encountering?
  
  Sudden disconnections from the VPN
  “Opening tun interface failed badly. Error: Cannot create interface”
  “Sorry, your device is missing a component called the “TUN driver”.”
  “Failed to add fwmark rule (Device or resource busy)”
  “HTTP proxy support only works for TCP based connections”
  “ERROR: Cannot open TUN”
  Cannot connect after upgrading Android OS