Same thing happened to me at an event this past weekend, in the USA. Helix was plugged into a power conditioner, which itself was on a circuit powering nothing other than a monitor and someone's iPhone. Absolutely no reason to believe it wasn't getting proper power. Suddenly turned off, then turned back on and "strobed" for a while before shutting down for good, at which point, we could all smell smoke clearly coming from the unit. I have a support ticket open and plan to have it repaired; suspect a blown capacitor, but will report back when I know.
And yes, of course you should always have a backup rig (the band bought a spare HX Stomp since all 3 guitarists are using Helix).
Love to hear if anyone else had this issue or has had it diagnosed.