There should be only one "real" series service running in a cluster, because it depends on a solr index. Having two would lead to inconsistencies, because each index would contain different information.
On the other hand, only "real" series should register in the service registry. The remote implementations are mere proxies for other OSGI bundles, and therefore the service registry ignores them.
In sum, in a Matterhorn cluster, there should only exist one active series service.
However, if one runs the following SQL in the database:
select * from mh_service_registration where path = "/series";
, several entries appear. One of then has the right type ("org.opencastproject.series"), but others have the type "org.opencastproject.series.remote". This happens because the "-remote" implementations of the series service incorrectly register themselves in the service registry.
The solution is simply removing two configuration keys in the OSGI_INF directory. The presence or absence of such keys tells the service registry whether or not to register the service.