Hi,

In file:
https://github.com/mongodb-js/mongodb-core/blob/d40cb87ad415cfe224ae00d7696fc549fbbd0c62/lib/connection/msg.js#L105

 header.writeInt32LE(this.requestId, 4); // requestID

requestId is used to write 2 bytes into header, but there is no limitation on how big this.requestId can be. It is growing with every message:

https://github.com/mongodb-js/mongodb-core/blob/d40cb87ad415cfe224ae00d7696fc549fbbd0c62/lib/connection/msg.js#L133

Msg.getRequestId = function() {
  return ++_requestId;
};

And so, eventually it will reach maximum allowed value +1 (I guess 32767+1).

As node documentation is saying:

https://nodejs.org/api/buffer.html#buffer_buf_writeint32le_value_offset

value should be a valid signed 32-bit integer. Behavior is undefined when value is anything other than a signed 32-bit integer.

In reality it means error which cannot be fixed even by re-connection to database:

TypeError: "value" argument is out of bounds
at checkInt (buffer.js:1185:11)
at Buffer.writeInt32LE (buffer.js:1375:5)
at Msg.toBin (/node_modules/mongodb/node_modules/mongodb-core/lib/connection/msg.js:105:12)