Here’s what Cervelo say happened to Heather:
*“The good folks from Cervelo and an expert from Shimano took a good look at my bike this afternoon. Turns out the actual Di2 failure was a 1 in a never seen before problem with the shifting mechanism within the derailer. It had nothing to do with the electronics - the signal was arriving but the worm gear that drives the shifting was somehow broken/shredded (possibly by an impact, loads of riding, then another impact - in transition somehow? A final straw kind of deal, which is why it worked fine the day before and to start on race day, but snapped during the ride). Basically just incredibly unlucky and there was nothing I could do to fix it.”