None of the locations I know of for changelogs/release notes are showing anything for 1.2.1: 

• https://plugins.jenkins.io/blueocean
• https://wiki.jenkins.io/display/JENKINS/Blue+Ocean+Plugin
• https://github.com/jenkinsci/blueocean-plugin/compare/blueocean-1.2.0...blueocean-1.2.1