That is because IC2 is outdated as a mod in general. The reason GreTeche exists at all is because IC2 is outdated and imbalanced, when was the last meaningful content patch for IC2? It was before most people starting with IC2.
With the latest update soul shards no longer spawn wither skeles. If you drag a normal skele spawner (one from a dungeon) to a fortress it will work don't know about the bees hope this helps!
