Kubernetes Service not distributing the traffic evenly among pods
Based on the information provided I assume that you are using http-keepalive which is a persistent tcp connection.A kubernetes service distributes load for each (new) tcp connection. If you have persistent connections, only the additional connections will be distributed which is the effect that you observe.
Try: Disable http keepalive or set the maximum keepalive time to something like 15 seconds, maximum requests to 50.