The SDAM spec says that a network timeout error that occurs before the connection handshake completes MUST reset the server to Unknown. MongoClient does not follow this rule:

If there is a network error or timeout on the connection before the handshake completes, the client MUST replace the server's description with a default ServerDescription of type Unknown, and fill the ServerDescription's error field with useful information.

https://github.com/mongodb/specifications/blob/bc864e6/source/server-discovery-and-monitoring/server-discovery-and-monitoring.rst#network-error-when-reading-or-writing