It seems Netbox retains the list of groups that a user belonged to when they first registered (or were imported into Netbox?).
Changes to the user's groups do not reflect in the user's profile in Netbox even days after they have been done.
LDAP:
$ id uid=20036(gtirloni) gid=500(wikidev) groups=500(wikidev),700(ops),1003(wmf),50062(project-bastion),50380(project-tools),52708(project-admin),53851(tools.gtirloni-sandbox)
Netbox:
Groups tools.admin, project-cloudinfra, project-tools, project-admin, project-bastion, tools.gtirloni-sandbox, ops, wmf, project-testlabs, project-toolsbeta, project-project-proxy, project-shinken, project-deployment-prep, project-wmflabsdotorg, project-codesearch, tools.openstack-browser, project-analytics, project-admin-monitoring, project-paws, project-qna, project-cvn, project-packaging, project-openstack, project-clouddb-services, project-cloudstore