The last company I worked for, we noticed that one of the servers in our Reading office kept going offline at a particular time each morning (anyone in IT probably knows where I'm going with this). We found out in the end, that one of the cleaners was vacuuming the Comms room and kept unplugging one of the Fileservers. Needless to say, all unattended cleaners were banned from that point on. That's probably what's happened here.