Whilst the CRCN transaction is monitoring the resource managers, you should consider the following:
Dynamic XA is more efficient than static XA, because the xa transaction is effectively started when the application accesses the resource manager; however static XA might be required if the application is not intercepting lost connections, or does not take appropriate action to signal to the system administrator that the connection to an RM has been lost, such as when a transaction ABENDs, or sends severe errors to the console.
If there are long-running tasks in the system, ensure that they regularly pass the control back to the system. For a CICS transaction, this means executing an EXEC CICS so that the system gets the opportunity to process the xa request sent to each process by CRCN. Failure to pass control back to the system causes the process emitting the request to wait until its request has been processed in all SEPs. If these requests are not processed immediately, CRCN waits until they are.