Currently when ismaster fails, the exception class is not logged. For example, the driver can produce this message when it is instructed to use a nonexistent path with ssl_ca_cert option:

MONGODB | Error running ismaster on localhost:27741: system lib

The "system lib" part is coming from openssl. With the exception class included, the message looks like this which immediately identifies the source of the problem:

MONGODB | Error running ismaster on localhost:27741: OpenSSL::X509::StoreError: system lib

This situation was encountered by a SO user in https://stackoverflow.com/questions/58053353/ibmcloud-how-can-i-connect-to-mongodb/58071056.