Why is it that in a threaded call to the gRPC function, when another user is added, the speed of receiving a response drops sharply, but the speed according to the logs in the service is the same?

Question

RPC

I implemented an asynchronous gRPC method with a flow in both directions, but for some reason, with 1 user with synchronous sending of messages, the speed is 4 seconds to get a complete and accurate answer, but it’s worth adding a 2nd user, the speed takes off 10-20 seconds to get a complete answer.
At the same time, nothing has changed in the service logs in terms of speed.