Looking around the web, it seems this means that the rate of voltage change on the input was too high. It could be loose connection, but it could also just be the utility voltage changing too fast. It does change throughout the day, between about 220v and 235v (I'm monitoring the SNMP stats).
I've reduced the sensitibity from "normal" to "reduced", as everything it's powering have switched-mode power supplies so don't really care too much about the input voltage or it's rate of change.