Slowdown when using TCPServer on Raspberry Pi4 / buster

I’m experimenting a strange behavior with TCPserver under RaspberryPi4/buster. When there’s a client connected, the FSP drop from 60 to ~25. When the client disconnect, FPS get back to full rate. Same program tested with linux (ubuntu/fedora) but not on raspberry runs fine.
Here’s some code snippets:

void ofApp::update(){
  checkNetworkMessage(TCPserver);
  ...
}

The function is:

void ofApp::checkNetworkMessage(ofxTCPServer &_TCPServer){
  string msg = "";
  for(int i=0; i < _TCPServer.getLastID(); i++){
      if(_TCPServer.isClientConnected(i)){
          msg = _TCPServer.receive(i);
          if(msg != "") {
              ofLogVerbose() << msg << " received";
              ofSendMessage(msg);
            }
        }
    }
}

Probably a thread to check for network messages should be a preferable solution, but i’m expecting something like one message/minute…
Any hints?

Thanks!

The same behavior happens with default example
communication/networkTcpServerExample
so it looks like a bug, in OF or ofxNetwork addon