Modded server hosted with NGROK, was working fine until i switched up the world. Crash report: https://pastebin.com/NqKjHVqA
Corrupted world, restore from backup.
I've changed the world multiple times and the same thing comes up.I fixed it by changing the superflat prefix from iron blocks to sandstone, no clue why that would effect anything
Do newly created worlds work? Does the world work in singleplayer?
Did you close the server before changing world?