I think your singlton cluster was not properly configured. Pls ask AS team for help.
Why should the cluster not correctly configured. It runs most of the time without problems. Just in special scenarios, the singleton MDB did not come up, if the node it is currently running on stopped.
The deploying and loading of MDB is beyond JBM, it should be part of AS configuration. That's why I recommended you to ask them to get better help.