Gitlab UI - Admin attempting to launch backgroup job resulting in 'Forbidden' message.

Gitlab UI started returning a 'Forbidden' screen message when attempting to 'enqueue' a background job, e.g. ldap_group_sync_worker, after we upgraded our installation from 9.2.3 to 9.5.10. We are currently on release 11.2.3-ee running on a Linux RHEL 7.5 server.

Production Log shows
Started POST "/admin/sidekiq/cron/ldap_group_sync_worker/enque" for 10.9.16.9 at 2019-03-04 10:51:45 -0500
with no other related entries for the submission of the request.