Hi. I experienced this with two of my eventides, all of which had original power supplies.
I have no idea what caused it specifically, but since i changed power supply (got a custom made on) it hasn´t occured.
I think the Eventide power supplies might be a bit frail, or underpowered, or at least something that leads to them powering off/on randomly.
Might be worth Eventide noting that this is an issue, and yes, i know of the PowerFactor, and if it wasn´t that expensive, i would have bought it.
Mind you, its a bit wierd that it doesn´t power all 4 (now 5) of the boxes.
Anyhoo, really happy with my Stompboxes, but the power supplies seems to cause alot of problems.