Attaching additional network ports to running VM does not work with API calls and detaching yields PortNotFound in Red Hat OpenStack Platform

Issue

Attaching additional network ports to running VM does not work with API calls and detaching yields PortNotFound in Red Hat OpenStack Platform.

The port is shown as attached in Openstack - but is not plugged to VM in reality.

Detaching/re-attaching such port is not possible with the API, but works with the nova/neutron CLI commands.

The log ERROR message that is observed when trying to detach the port via API is:

nova-compute.log.1:2019-04-22 10:41:53.247 1 ERROR oslo_messaging.rpc.server PortNotFound: Port 6836ddfe-246e-4705-98ab-ccc9332c3888 is not attached