There was a Z-Stream upgrade on acs-prod-eu-01 on Feb 17th. 

The SLI dashboard usually shows the graphs annotated with Openshift/Kubernetes upgrades, so we can associate SLI drops with a cluster upgrade.

The annotations are based on a prometheus query that detects if the gitVersion of the Openshift/Kubernetes apiServer has changed. In this case, this Z-stream upgrade did not change the gitVersion of neither Kubernetes or Openshift.

Investigation found that the node's kernel version was changed. This metric is available in prometheus as well under node_info. The dashboard annotation query should be modified to also detect kernel version upgrades.