Both Participants are on Desktop.

Participant A: 
- OS: MacOS version 10.15.3
- Browser: Safari version 13.0.5

Participant B: 
- OS: Windows 10 Pro N version 1903
- Browser: Chrome version 80.0.3987.122

Participant A has onnegotationneeded event defined as: 

async function negotiate(e) {
  let offer;
  offer = await pc.createOffer();
  await pc.setLocalDescription(offer);
  //send offer to remote with websocket
}

If participant A creates a offer with audio only stream, and remote participant B creates an answer with audio only stream also, the connection is established.
After Participant A adds a video stream with RTCPeerConnection.addTrack(), participant B's RTCPeerConnection.ontrack event doesn't fire.
Also Participant A doesn't fire onnegotationneeded event, if I manually call RTCPeerConnection.createOffer() after calling addTrack, remote participant B's ontrack event fires.