The broken chain syndrome, or derailed chain syndrome, that has plaqued Nambotin recently is a lot more common problem at the EWC /WEC level than most people realize.
I've attended a half dozen or so EWC / WEC events in my lifetime and a can recall seeing at least one chain incident at each event.
EWC / WEC riders, especially their better riders, have a tendency to run a very loose chain tension especially with the addition of the more extreme style tests with its trials course like terrain.
Riders at this level are looking for every advantage and feel their rear suspension works better when the chain is run just a little looser than you and I would run it so there is zero chance of it binding when the rear suspension is completely collapsed and the drive system is under load.
They obviously start the two-day event with a new chain and sprockets and a very loose chain for reasons stated above. If the mechanic and/or the rider aren't paying close attention to the chain tension at every technical service they can get into trouble in a hurry as the chain stretches slightly and the sprocket start to wear-in and before you know it there is a chance the chain can be easily deflected off the sprockets.
Should Nambotin start using a different chain guide, I'm not sure that's his biggest problem. He, and his mechanic, most likely should pay closer attention to their chain tension at every check.