Jiggling the wheel or shift lever does nothing. When the key cannot be inserted or must be forced it is as though the "door" in the key slot is stuck closed or blocked by another part. Once the lock starts working again, it is perfectly smooth. I am leaning toward a fleck of metal or a burr inside the lock, or one of the cable locks preventing the door opening or the cylinder turning..though I do not know if the mechanism is built that the former explanation is valid.