tunnel server连接远程agent报错

请问启动agent并注册到了tunnel server，并生成了agentId，但是在连接远程agent的时候报错。是什么原因呢？

2021-03-13 22:52:48.314 INFO 120524 --- [Server-boss-1-1] io.netty.handler.logging.LoggingHandler : [id: 0xe4c29c18, L:/0:0:0:0:0:0:0:0:443] READ: [id: 0x146bba14, L:/11.33.182.224:443 - R:/11.93.232.206:9588]
2021-03-13 22:52:48.314 INFO 120524 --- [Server-boss-1-1] io.netty.handler.logging.LoggingHandler : [id: 0xe4c29c18, L:/0:0:0:0:0:0:0:0:443] READ COMPLETE
2021-03-13 22:52:48.409 INFO 120524 --- [rver-worker-3-3] c.a.a.t.server.TunnelSocketFrameHandler : websocket handshake complete, uri: /ws?method=agentRegister&arthasVersion=3.4.7-SNAPSHOT&id=11-93-232-206
2021-03-13 22:53:04.474 INFO 120524 --- [Server-boss-1-1] io.netty.handler.logging.LoggingHandler : [id: 0xe4c29c18, L:/0:0:0:0:0:0:0:0:443] READ: [id: 0xa8926d23, L:/11.33.182.224:443 - R:/100.124.25.136:59430]
2021-03-13 22:53:04.474 INFO 120524 --- [Server-boss-1-1] io.netty.handler.logging.LoggingHandler : [id: 0xe4c29c18, L:/0:0:0:0:0:0:0:0:443] READ COMPLETE
2021-03-13 22:53:04.480 INFO 120524 --- [rver-worker-3-4] c.a.a.t.server.TunnelSocketFrameHandler : websocket handshake complete, uri: /ws?method=connectArthas&id=11-93-232-206
2021-03-13 22:53:04.481 INFO 120524 --- [rver-worker-3-4] c.a.a.t.server.TunnelSocketFrameHandler : try to connect to arthas agent, id: 11-93-232-206
2021-03-13 22:53:04.481 INFO 120524 --- [rver-worker-3-4] c.a.a.t.server.TunnelSocketFrameHandler : random clientConnectionId: GRPPBAALSKPNNHHZCGAE
2021-03-13 22:53:04.481 INFO 120524 --- [rver-worker-3-4] c.a.a.t.server.TunnelSocketFrameHandler : startTunnel response: response:/?method=startTunnel&id=11-93-232-206&clientConnectionId=GRPPBAALSKPNNHHZCGAE
2021-03-13 22:53:04.485 INFO 120524 --- [rver-worker-3-4] c.a.a.t.server.TunnelSocketFrameHandler : browser connect waitting for arthas agent open tunnel
2021-03-13 22:53:24.485 ERROR 120524 --- [rver-worker-3-4] c.a.a.t.server.TunnelSocketFrameHandler : browser connect wait for arthas agent open tunnel timeout, agentId: [11-93-232-206], clientConnectionId: GRPPBAALSKPNNHHZCGAE

Start with the TunnelSocketFrameHandler log sequence for agentRegister, connectArthas, and the startTunnel response. Reproduce the remote-agent connection and investigate why the agent does not open the tunnel before the 20-second timeout. Done means identifying the cause and documenting a verified resolution.

Written by the indexing model from the issue text.