From RHOL 5.5.3 the field message is deleted when "parse: json" is enabled.

You can find the change in this bug–> https://issues.redhat.com/browse/LOG-2759

"Before this update log entries that had structured messages included the original message field which made the entry larger. This update removes the message field for structured logs to reduce the increased size."

But in the official documentation we can find: "When you enable parsing JSON logs by using parse: json, the CR copies the JSON-structured log entry in a structured field, as shown in the following example. This does not modify the original message field." [1] [2]

[1]https://docs.openshift.com/container-platform/4.10/logging/cluster-logging-enabling-json-logging.html

[2]https://docs.openshift.com/container-platform/4.11/logging/cluster-logging-enabling-json-logging.html