@Jonathan -- as you can see that ndb-client hangs I assume you have shell access when its broken. If so can you strace the ndb-client to see what it was trying to do when it gets stuck? What its last system call is. Also is anything emmitted into dmesg related to the hang; please wait long enough for the 120 second 'its stuck' timer to fire and report issues.
As this is hanging with the client in a D there may be a kernel componet here. I have had a look and little has changed since Maverick (where I am assuming it worked). There has been some locking work for BKL removal which may be related, difficult to say.