Lucifer_6_6_6_

Hi, I just started my own Tekkit Classics server on a Linux Ubuntu server 20.04 vm on Proxmox. The players complain about seeing through the world, the only see some lava pits. I mostly happens when they are mining. It isn't from their end I think, its also not a hardware problem on my server, I have 16GB RAM and a 500GB HDD and backup on a 4TB RAID configuration. I run this version: Craftbukkit version git-Bukkit-jenkins-CraftBukkit-173 (MC: 1.2.5) (Implementing API version 1.2.5-R4.1-MCPC-SNAPSHOT) Is this a bug from Tekkit Classic? Or is it because of their hardware? I know some of them have a very good gaming desktop. Kind regards and thanks in advance, Piet