Receiving OpCode -101 from Sender -2 after connecting Unity client

On a RTS/Unity project, my Unity Client can connect to the server and receives the message sent by onPlayerAccepted(). The connection can not last for over a minute, sometimes closing as soon as 30 seconds in. My client’s onErrorEvent is then triggered:

[server-sent] OnErrorEvent - Sender: -2 OpCode: -101 data:

and from the server side:

13 Mar 2022 23:03:23,67 [WARN] (index.js) 133: Player 1 did not respond to the last ping. Terminating the player client.
13 Mar 2022 23:03:23,67 [INFO] (ws.js) 206: TCP client connection for player: 1 is terminated by the server

I see no AWS documentation or anything on a negative value for sender, or a -101 opcode. I do not have any negative opcodes defined in my server code. Where does this come from?

I see that this has been resolved in Client not receiving RTS message - #10 by _Chris, let us know if you have any other questions regarding the topic!