RDS automatic minor version upgrades have been disabled for the affected DB Instance.
Amazon RDS allows you to control if and when the relational database software powering your DB Instance (i.e. MySQL) is upgraded to new versions supported by Amazon RDS. This provides you with the flexibility to maintain compatibility with specific MySQL versions, test new versions with your application before deploying in production, and perform version upgrades on your own terms and timelines. By default, your DB Instance will automatically be upgraded to new MySQL minor versions as they are supported by Amazon RDS. Since major version upgrades involve some compatibility risk, they will not occur automatically and must be initiated by you.
In the context of MySQL, version numbers are organized as follows:
MySQL version = X.Y.Z
X = Major version, Y = Release level, Z = Version number within release series.
From the Amazon RDS standpoint, a version change would be considered major if either major version or release level is being changed. Example: going from 5.1.X -> 5.5.X. A version change would be considered minor if the version number within the release is being changed. Example: going from 5.1.45 -> 5.1.49.
Consider whether you would like AWS to automatically upgrade to minor versions on your database instance. Modify your settings to allow minor version upgrades if possible. If you wish to turn on automatic version upgrades, you can do so by setting the AutoMinorVersionUpgrade parameter to “true.”