The release notes can be found here for driver version 2.4.0:
https://github.com/mongodb/mongo-ruby-driver/releases/tag/v2.4.0
and here for bson gem version 4.2.0:
https://github.com/mongodb/bson-ruby/releases/tag/v4.2.0
Both are available from RubyGems:
gem install mongo
gem install bson
Please report any issues in our Jira project: https://jira.mongodb.org/browse/RUBY
Thanks
Emily