i experienced this morning after an update similar problems, but uncommented (#) the directive in traffic-dfl.conf.
Just after getting nginx up and running, there was another update (IMHO grommunio-admin-common) and this replaced traffic-dfl.conf again (my # was gone) and it was running.
Relatively new (30.10.25) is /usr/share/nginx/modules/mod_vts.conf (Grommunio Appliance, Community Edition), which loads the module ngx_http_vhost_traffic_status_module.so