I've never experienced this, so I'm sure this post will be of marginal usefulness at best, but I'm posting anyway.
It sounds like something to be wary of, but not overly concerned with. Sure, it would suck if it happened again in the middle of a wedding, but you know a fix, which can easily be applied in a pressure situation if need be. And if it happens again, then I'd say it might be worth sending to Canon for a checkup.
But these things happen- they happen to my computer, they happen to my phone, and they happen to the microscope in my lab. Every so often, random chance will cause a kernel panic, and once you do a hard reboot, and everything gets a fresh start, the problem is resolved. It's totally software based (well, probably a bit quantum, really, I've always suspected it was a matter of a totally normal logical process getting disrupted by current fluctuations or something), and nothing's wrong with your hardware. If it's been 3 years, then your camera will probably be due to misbehave again in another 3 years... or maybe 8 years, or maybe 6 months.
And, maybe you know all this anyway, and this post was totally useless because I couldn't corroborate this behavior. But I said that up top, so you didn't have to read it all. ;-)