Any idea why modded content will occasionally completely despawn?

[Andy Ollom 0]

I'm running the Island with 16 mods including S+, and 2 times since I started the server ALL mod items and structures disappear as if the server skipped over the mod loading stage. The mod list still has all the ID's and joining still required loading all of them, but anything added by mods in the inventory, dino inventories, and structures simply ceases to exist. Any thoughts on the matter? I've had to roll back stuff, but still lost my inventory because I didn't know to use FTP to restore the character backups.