bit more detail from the log
Sep 4 19:19:08 MvB Metabase: INFO util.ssh :: creating ssh tunnel firstname.lastname@example.org:22 -L 62865:sqlsrv6:3306
Sep 4 19:19:08 MvB Metabase: ERROR metabase.driver :: Failed to connect to database: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
The tunnel shows port 62865, I think it should be 3306.