Y2K
My recollection is that in fact there were no real issues, or almost none.
Which is entirely due to the considerable effort put in by my colleagues and I, and other engineers in other companies, to find and fix problems well before 1/1/2000.
Of course, we could have just waited to see what went wrong and fixed it then. Based on the bugs that we did fix I can assure you that it wouldn't have been a non-event then, believe me. Perhaps you'd have preferred that?