Why is RTCPeerConnection.iceGatheringState always gathering information when answering. Instead of completing

Question

I'm using jssip version 3.10.1 and when answer, I set up the stun server with the following code.

RTCSession.answer({
          mediaConstraints: { audio: true, video: false },
          pcConfig: {
            iceServers: [
              {
                urls: [
                  "stun:stun.l.google.com:19302",
                ],
              },
            ],
          },
        });

After the incoming call, I executed this method, but the sip signaling return is very slow, nearly a minute to return 200, during the iceGatheringState state has been gathering, rather than complete, this is why, please enlighten me!

For the above problem, I have tried using the web program on different computers, and the result I get is that some computers are answering incoming calls normally, while others are not answering incoming calls with the above message