Getting javax.ejb.ConcurrentAccessTimeoutException WFLYEJB0241 on Singleton EJB in JBoss EAP 8 / 7 / 6

Issue

• Our @Singleton EJB is logging this exception in EAP 7:

ERROR [org.jboss.as.ejb3.invocation] (ServerService Thread Pool -- 208) WFLYEJB0034: Jakarta Enterprise Beans Invocation failed on component MySingletonEJBImpl for method public abstract void com.redhat.examples.MySingletonEJB.invoke(java.lang.String): javax.ejb.ConcurrentAccessTimeoutException: WFLYEJB0241: Enterprise Beans 3.1 PFD2 4.8.5.5.1 concurrent access timeout on MySingletonEJBImpl - could not obtain lock within 5000MILLISECONDS
  at org.jboss.as.ejb3.component.singleton.ContainerManagedConcurrencyInterceptor.processInvocation(ContainerManagedConcurrencyInterceptor.java:102) [wildfly-ejb3-7.4.0.GA-redhat-00005.jar:7.4.0.GA-redhat-00005]
  at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:422)
  ... 

• Getting exception like below.

javax.ejb.ConcurrentAccessTimeoutException: JBAS014373: EJB 3.1 PFD2 4.8.5.5.1 concurrent access timeout on org.jboss.invocation.InterceptorContext$Invocation@7d5446 - could not obtain lock within 5000MILLISECONDS
org.jboss.as.ejb3.concurrency.ContainerManagedConcurrencyInterceptor.processInvocation(ContainerManagedConcurrencyInterceptor.java:100) [jboss-as-ejb3-7.3.0.Final-redhat-14.jar:7.3.0.Final-redhat-14]
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation-1.1.2.Final-redhat-1.jar:1.1.2.Final-redhat-1]
    ...

• Having the error above even if the class is annotated with @Lock(READ)

@Singleton
@javax.ejb.Lock(javax.ejb.LockType.READ)
public class MySingletonBean {

    public void aReadMethod() {...}
    @javax.ejb.Lock(javax.ejb.LockType.WRITE)
    public void aWriteMethod() {...}
}