Some MySQL connectors fail to start due to a ConfigException (new implementation)

Upon upgrading from 1.3 to 1.5.4 some of our MySQL connectors failed due to the following exception:

org.apache.kafka.common.config.ConfigException: Invalid value org.apache.kafka.common.errors.InvalidConfigurationException: Schema being registered is incompatible with an earlier schema; error code: 409 for configuration Failed to access Avro data from topic our-db-name-avro 

This looks to be on the Schema Change Topics for those connectors.

Reverting to the old implementation using internal.implementation=legacy is a workaround for the issue.

I confirmed the schema incompatibility in the Schema Registry log file (running at DEBUG log level). See attached file.