Unexpected factors such as power outages and accidental disconnects require additional preparation to ensure throughput.
When the engine encounters a critical problem during processing, it suspends. You will be notified of this on the screen. "Suspending" means the engine has stopped processing; however, the application process is still running: all current processes and events remain instantiated in the applications process space, but it is in a holding pattern. If the cause of the suspension is something small, i.e., the output queues some process have reached capacity, you can correct the problem (such as in this case drain the queue), enter resume, and all processing continues.
If the problem is more severe, the engine can be shutdown. When it is shutdown the engine gracefully closes its queue and database connections before ending the application process. Whether the engine is shutdown or takes a hard shutdown, the recovery is the same.