Periodically (once per minute) check client NetSpeed and if it less from maximal server speed, notify player:
If player write in chat !FixSpeed, then his speed increased to server value.Your network speed is too low (8000 < 50000). To fix game lags, write to the chat: !FixSpeed
Install:
Add to mutator list FixNetSpeed.FixNetSpeed (or to ServerActors - preferred way)
Add to ServerPackages FixNetSpeed.