I don't think so because it happens outside of work hours too. It's all very random and happens at random times of the day; sometimes in the middle of a shift, sometimes in the middle of the night.
Well, the actual check seems to fire rather intermittently since I didn't alter the check interval, so that would explain why it seems to happen at random times if you somehow trigger a check in the middle of the night. I assume that, when they disappear from the list and you go and make them active, they are NOT, in fact, at the office?