What does it mean when there is still water in the autoclave chamber after a cycle?

When it is vented when the pressure is high, the chamber is almost dry, but if the pressure drops too much (ie too much time passes) the chamber eventually loses pressure. Does this mean the items are not sterile anymore? I haven't found anything that explains this, it just says to contact a supervisor if it happens. I'm curious about why this is a problem. Thanks!