First, test your baseline speed

Before troubleshooting, find out if the problem is the VPN or your internet connection:

  1. Disconnect the VPN
  2. Run a speed test at fast.com or speedtest.net
  3. Connect the VPN
  4. Run the same test again

A VPN will always add some overhead. Expect a 10 to 30% speed reduction compared to your raw connection. If you are seeing a 70%+ reduction or speeds under 5 Mbps, there is a problem worth investigating.

Common causes and fixes

1. Distance to the server

The farther the server, the higher the latency and lower the throughput. This is the most common cause of slow speeds.

Fix: Switch to a server closer to your physical location. In Happ, enable Auto Select to automatically connect to the fastest server. Or manually pick a server with the lowest ping time from the server list.

2. Protocol choice

Different transport protocols have different performance characteristics:

ProtocolSpeedStealthBest for
xHttpFastGoodMost networks. Start here
gRPCMediumExcellentHeavily filtered networks
WebSocketMediumGoodCorporate or school networks

Fix: Try switching protocols in your app settings:

  • Happ: Settings > Connection > Transport protocol
  • v2RayTun: Settings > Protocol > Select a different transport

If xHttp is slow, try gRPC. If gRPC is slow, try WebSocket.

3. Network congestion

Your local ISP or the VPN server may be congested during peak hours.

Fix:

  • Try a different time of day (off-peak hours are usually faster)
  • Switch to a less popular server region
  • Try a server in a different country nearby

4. Device or app limitations

Older devices or outdated app versions may not handle high-speed encryption well.

Fix:

  • Update your VPN app to the latest version (check the app store or happ.su)
  • Close bandwidth-heavy apps (streaming, large downloads) while testing
  • Restart your device to clear network cache

5. MTU issues

Large packets may be getting fragmented, which slows down the connection. This can happen on some network configurations.

Fix:

  • Happ: Settings > Advanced > MTU > Try 1400 or 1300
  • v2RayTun: Settings > Advanced > Set MTU manually to 1400
  • v2rayN: Settings > Core settings > Adjust MTU

6. Battery or power saving mode

On mobile devices, power saving mode can limit CPU performance and slow down VPN encryption.

Fix:

  • Disable battery or power saving mode while testing
  • Add the VPN app to your battery optimization whitelist (Android) or disable Low Power Mode (iOS)

Speed test checklist

Work through these in order:

  1. Test without VPN to confirm your baseline speed
  2. Try 3 different server regions
  3. Try 2 different transport protocols (xHttp and gRPC)
  4. Update your VPN app to the latest version
  5. Test on a different network (for example, switch from Wi-Fi to mobile data)
  6. Restart your device and test again

If speeds are consistently slow across all servers and protocols, contact support@sericavpn.com with your test results. Include your device model, app version, and the server regions you tested.