User may need to enable the utf8 conversion filter

NOTE: using oc edit ds/logging-fluentd or otherwise editing the fluentd daemonset configuration may trigger the redeployment of fluentd on every node in the cluster.  If you do not want to do that, then use

oc label node $the_node logging-infra-fluentd-

for each node to turn off fluentd gradually.

Then

oc edit ds/logging-fluentd (or use the console UI to edit the fluentd daemonset)

In the env: section, add the following:

        - name: ENABLE_UTF8_FILTER
          value: "true"

Make sure to preserve the indentation, and the "true" must be in double quotes, or it will be interpreted as a YAML boolean value.

https://github.com/openshift/origin-aggregated-logging/blob/release-3.6/fluentd/run.sh#L315

Then, restart fluentd on each node

oc label node $the_node logging-infra-fluentd=true

Forced UTF-8 encoding caused a performance regression and was made 'opt-in' as part of [1]. Please see c#2 to see if this resolves your issue and close if so.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1513254

User behind this bz confirmed that the suggested solution #2 works for them. Thanks for clarifying; closing this bug report.