Gremlins! This is computer nerd 'speak' for the fact that systems, especially complex systems, will experience a wide variety of issues that could be promulgated by hardware dying, usage peaking, upgrade activities going South, hackers infiltrating, yada, yada, yada. If one could have had a peak behind the curtains, one would likely have noticed some administrators cursing as they rush to fix whatever problem caused the links to fail and patted themselves on the back when things were set straight.