Just as a note, NaNs are usually random, because raytracing has randomness in it. Sometimes, the exact rays that caused the NaN do not happen - but sometimes they do. If the scene ever gave a NaN, and nothing was fixed or changed, then chances are it will come back again at some point (and then go away again, and so on). So, as a better safe than sorry, still best to submit the scene so we can look into it :)