So far, it's happened twice while I was online today. The entire server goes down for a minute or two, with a Java error message. This wouldn't be too big of an issue, but some items in the inventory are lost. More accurately, the inventory is restored to a previous point in time; new items are lost, and old items remain. Oddly enough, physically placed blocks are not affected.
However, I noticed that it last happened exactly at 9:00 PM EST, about 10 minutes ago. I'm beginning to wonder if there's a setting or something on the server itself, that makes it reset every so often. If so, can it be disabled, or is there any way to predict it, at the very least?