This is a day-0 bug in NETCONF server implementation: at least the event time, and most likely the entire NetconfNotification document, mishandles its namespace.

The problem is with NetconfNotification.NOTIFICATION_NAMESPACE, introduced here: https://git.opendaylight.org/gerrit/c/controller/+/14921/5/opendaylight/netconf/netconf-notifications-api/src/main/java/org/opendaylight/controller/netconf/notifications/NetconfNotification.java#24

The namespace points to the Notification CAPABILITY URN:

urn:ietf:params:netconf:capability:notification:1.0

not to the Notification XML Namespace URN:

urn:ietf:params:xml:ns:netconf:notification:1.0

The latter needs to be used, as exemplified in https://datatracker.ietf.org/doc/html/rfc5277#page-27