Difficult to say based on the information provided. Always ask yourself this, if you were in support, would this information you provide help you figuring out the problem?
Provide some information on how your system is setup like...
Requestlisteners for incoming, if any processing is done there, transaction manager and number of sessions, logs when processing stopped.
Were requests making it to the transaction manager?
Were participants blocking or stuck somewhere (jpos profiler info in the logs will help you see that)?
Logs have a lot of details that can assist in debugging the problem.