mafalda is up now.
I found that the cable for mafalda (the sole red cable) had a broken latch.
The cable was about falling off from the switch. As a first-aid, I used this technique to put a new latch, and put it into the switch.
Now I can logged in it. I did not rebooted it.
I am guessing that the NFS file system hangup may have caused some machines to get into an awkward state. We may be best off doing a controlled power cycle of everything...