This problem occurs after you upgrade all of the nodes in your cluster to
6.6.1 by using rolling upgrades. When you try to use machine learning features for
the first time, all attempts fail, though
GET _xpack and
indicate that X-Pack is enabled.
Errors when you click Machine Learning in Kibana.
Jobs list could not be createdand
An internal server error occurred.
Null pointer and remote transport exceptions when you run machine learning APIs such as
Errors in the log files on the master nodes.
unable to install ml metadata upon startup
After you upgrade all master-eligible nodes to Elasticsearch 6.6.1, restart the current master node, which triggers the machine learning features to re-initialize.
For more information, see Rolling upgrades.