Problem Summary: Once a multigroup is created using geomg create on any controller in a site, the multigroup gets created automatically on other clusters in the site if that controller has no site configuration synchronization errors with those clusters. If the site synchronization status is in ERROR between any such cluster and that controller, then that cluster does not accept the multigroup creation.
One possible way to attempt to resolve the site synchronization ERROR is by using the geosite update command on that cluster with the controller as an argument in order to make the site's configuration data on the cluster the same as the data that exists on the controller, and thereby replicate the multigroup onto that cluster. This replication of a multigroup configuration might fail in some situations even though the site synchronization status of that cluster will report OK with respect to the controller.
Workaround: Use the geosite leave command to make that cluster leave the site and then include it back in the site using the geosite add-member and geosite join commands.