If it keeps happening, it means something has gone wrong. XenForo doesn't really have the concept of a transient error due to external networking issue where you don't care if it happens once but do care if it happens a lot.Do we really need to see it as a server error though? Might be better to just handle it silently.
I see the same thing happen sporadically for gravatar and capacha services. Delete/ignore the error if it is a once off, worry if it happens often.