Could transient network issues or firewalls between the client and SQL Server contribute to Error 1326, or would they result in different errors?

Transient network issues or firewalls typically do not directly cause Error 1326 (Logon Failure). Network connectivity problems or firewall blocks usually result in different ODBC errors, such as 'SQLSTATE 08001' (SQLSTATE_COMMUNICATION_LINK_FAILURE) or 'A network-related or instance-specific error occurred while establishing a connection to SQL Server.' Error 1326 specifically indicates that a connection *was* established, but the authentication phase failed due to invalid credentials, rather than a failure to reach the server.