I've not seen that happen, but it something not really possible to investigate if there are no error logs and the issue is no longer present. I would advise if you see it happen again, let us know so we can investigate.
The most likely cause in situations like this, is an inability to write something to disk at the time. It being with both sites, it seems very highly unlikely to be the software, and more likely to be environment. After all, the chances of the same thing happening on both sites at the very same time is very unlikely.