EAP doesn't call ServiceLoader (META-INF/services/org.jboss.msc.service.ServiceActivator) when it is deployed in EAR/lib. The SingletonService (not a singleton EJB) is activated in the ServiceLoader so the SingletonService hasn't been activated from the first. It works as expected when deployed as an EJB (not in EAR/lib).

When the ServiceLoader is called, a message of "HATimerService will be installed!" is logged and the SingletonService will be activated.

$ fgrep -e HATimerService -e '[org.jboss.as.clustering.singleton]' domain/servers/server-one/log/server.log
12:14:52,373 INFO [org.jboss.as.quickstarts.cluster.hasingleton.service.ejb.HATimerServiceActivator] (MSC service thread 1-7) HATimerService will be installed!
12:14:56,251 INFO [org.jboss.as.clustering.singleton] (ServerService Thread Pool – 54) JBAS010342: master:server-one/singleton elected as the singleton provider of the jboss.quickstart.ha.singleton.timer service
12:14:56,251 INFO [org.jboss.as.clustering.singleton] (ServerService Thread Pool – 54) JBAS010340: This node will now operate as the singleton provider of the jboss.quickstart.ha.singleton.timer service
12:14:56,268 INFO [org.jboss.as.quickstarts.cluster.hasingleton.service.ejb.HATimerService] (MSC service thread 1-8) Start HASingleton timer service 'org.jboss.as.quickstarts.cluster.hasingleton.service.ejb.HATim
erService'
12:14:56,873 INFO [org.jboss.as.clustering.singleton] (notification-thread-0) JBAS010342: master:server-one/singleton elected as the singleton provider of the jboss.quickstart.ha.singleton.timer service