It looks like this page https://docs.redhat.com/en/documentation/openshift_container_platform/4.18/html/monitoring/troubleshooting-monitoring-issues#investigating-why-user-defined-metrics-are-unavailable_troubleshooting-monitoring-issues has appeared in OCP docs, a quick look at the history suggests it was only included in the managed OCP docs, before.

Was this change intentional, or could it be an error introduced during the migration?

Many of the procedures, on alerts, described there are already covered, or would be better suited in the runbooks https://github.com/openshift/runbooks, alerts should already link to the appropriate runbooks.