Since its earliest versions PyMongo has included the command document repr in the exception message when a command fails. The command document could include sensitive information (what "sensitive" means will differ from application to application). If the application using PyMongo logs tracebacks to a central location that could leak information (PyMongo does no logging of its own).

There is no useful information exposed by PyMongo itself (technically username could leak for certain authentication related commands, but only if authentication fails and a failure does not indicate if the username was correct). This can't be used to enumerate usernames and none of the authentication mechanisms are replayable.