[jccooper]

Hard to say what happened from the sketchy reports, but there's been some mention of "mechanical problems" due to lunar dust, and hibernation problems. I guess they have some mechanical movement involved in hibernation mode. Pre-positioning solar arrays, maybe? Storing instruments?

Lunar dust is notoriously abrasive, having formed in a non-erosive setting. It's a well known problem for lunar exploration, and NASA's done a lot of work on it. Not a lot of recent practical experience, of course.

The Chang'e designers must have known about the problem. Apparently they underestimated it, or just missed. Hopefully there's some good lessons learned for future missions. Getting there and working for a lunar day is a pretty good job in itself.