What driver are you using on that box? Is it the same as the others?
Certainly doesn't seem like it's too hot or
oc'd too much. Wonder why it's happening in batches like that, though. I could see the odd NaN if everything is ok, but 7 in a row seems to indicate something else.
We could take a look at the run-clone-gen numbers to see if there is any correlation. Do you still have the logs?