Describe the bug
I killed Wither, then tried to harvest Onyx.

Screenshots

Info (please complete the following information):

• Modpack Version: 3,0 Beta4
• Server or Singleplayer: LAN server
• Version the world was created on:3.0 Beta3

1. you're on a LAN server. LAN is not supported.
2. you didnt create a new world like we said you should