Problem writing data with NodeJS TLSSocket - node.js

Question

Background:
I have a NodeJS TCP stream server with SSL (tls server) which simply forwards data from client A to client B. i.e. it listens to connections on port 9000 (client A) and writes the received data to an existing persistent connection on port 9001 (client B). The connection between NodeJS and client B is persistent, never broken. Everything is running on my local machine.
Problem:
When using JMeter as client A and sending 300 requests (threads) with a ramp-up period of 1 second, a few requests never arrive at client B.
Troubleshooting done so far:
First I checked the logs of NodeJS application, which indicated that 300 requests were received from client A, and 300 requests were sent to client B.
Then I checked the logs of the client B, which indicated that only 298 requests arrived.
Next I monitored the local network using WireShark, which to my surprise indicated that 300 requests arrived from Client A to server, but only 298 of them were sent to client B.
Server side function which writes data to client B:
The function is a class member, where vSocket is a NodeJS TLSSocket which represents the persisted connection with client B. In the server logs, I get "Writing data to socket." and "Wrote data to socket." 300 times. I never get "Unexpected error while writing data to socket." or "Write returned false.".
public async SendAsync (pData: string): Promise<void> {
return new Promise<void>((pResolve, pReject) => {
try {
this.uLogger.Debug('Writing data to socket.', pData);
const rc = this.vSocket.write(pData, (pError) => {
if (pError) {
this.uLogger.Error('Unexpected error while writing data to socket.', pError);
return pReject(pError);
}
this.uLogger.Debug('Wrote data to socket.', pData);
if (this.vKeepConnectionOpen == false) {
this.uLogger.Debug('Not keeping this socket open.');
this.CloseAsync();
}
return pResolve();
});
if (rc == false) {
this.uLogger.Debug('Write returned false.', this.uId);
}
} catch (error) {
this.uLogger.Error('Unexpected error while writing data to socket.', error);
return pReject(error);
}
});
}
socket.write(data[, encoding][, callback]):
The docs say that -
Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory.
Since in my case this function never returns false, I assume NodeJS has successfully written the data to OS buffer, and the data should have been sent.
This problem is frequently replicable, and more likely to occur when I send hundreds of requests with JMeter. It is less likely to occur with 10 requests, and has never happened with < 5 requests.
I don't understand what's happening here, any help is appreciated.