Today the server crashed after it's usual reboot. Looking at the crash report, I blamed Traverse. After removing it, the server started normally. Not wanting to remove Traverse, I then used yesterday's server backup, which runs fine as well.

Whatever happened to kill the server, must have happened yesterday. Currently asking around what people have been up to yesterday, looking for clues. Unfortunately I don't have any logs from yesterday. Only from today.

I'll look into making it not crash in this situation, but from the error it looks like Biolith's game state was corrupted. That's stored using Minecraft's own game state mechanism, so it suggests to me you are wise to restore from backup anyway. The odds are good some other game data was also corrupted...