Does any of your EJBs have @PostConstruct methods that might hang waiting for some resources?
yes, I have lot of singleton and non-singleton beans with @PostContruct. In jboss7 I converted all service beans to singleton bean and service bean's start method was annotated with @PostConstruct .
Non singleton bean with @PostConstruct was as before. Is it the singleton bean with @PostConstruct creating the problem
Not sure. You might want to set a more verbose log level in order to see which bean it's trying to instantiate...