net.minecraft.util.ReportedException: Adding entity to track
    at net.minecraft.entity.EntityTracker.addEntityToTracker(EntityTracker.java:249) ~[EntityTracker.class:?]
    at net.minecraft.entity.EntityTracker.trackEntity(EntityTracker.java:171) ~[EntityTracker.class:?]
    at net.minecraft.world.ServerWorldEventHandler.onEntityAdded(ServerWorldEventHandler.java:39) ~[ServerWorldEventHandler.class:?]
    at net.minecraft.world.World.onEntityAdded(World.java:1232) ~[World.class:?]
    at net.minecraft.world.WorldServer.onEntityAdded(WorldServer.java:1176) ~[WorldServer.class:?]
    at net.minecraft.world.WorldServer.loadEntities(WorldServer.java:1132) ~[WorldServer.class:?]
    at cubicchunks.world.cube.Cube.onLoad(Cube.java:562) ~[Cube.class:?]
    at cubicchunks.server.ServerCubeCache.onCubeLoaded(ServerCubeCache.java:365) ~[ServerCubeCache.class:?]
    at cubicchunks.server.ServerCubeCache.lambda$null$1(ServerCubeCache.java:322) ~[ServerCubeCache.class:?]
    at cubicchunks.server.chunkio.async.forge.AsyncIOProvider.runCallbacks(AsyncIOProvider.java:59) [AsyncIOProvider.class:?]
    at cubicchunks.server.chunkio.async.forge.AsyncCubeIOProvider.runSynchronousPart(AsyncCubeIOProvider.java:65) [AsyncCubeIOProvider.class:?]
    at cubicchunks.server.chunkio.async.forge.AsyncWorldIOExecutor.tick(AsyncWorldIOExecutor.java:267) [AsyncWorldIOExecutor.class:?]
    at cubicchunks.server.chunkio.async.forge.AsyncWorldIOExecutor$1.onWorldTick(AsyncWorldIOExecutor.java:313) [AsyncWorldIOExecutor$1.class:?]
    at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_9__onWorldTick_WorldTickEvent.invoke(.dynamic) [?:?]
    at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90) [ASMEventHandler.class:?]
    at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:168) [EventBus.class:?]
    at net.minecraftforge.fml.common.FMLCommonHandler.onPostWorldTick(FMLCommonHandler.java:269) [FMLCommonHandler.class:?]
    at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:792) [MinecraftServer.class:?]
    at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:687) [MinecraftServer.class:?]
    at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:156) [IntegratedServer.class:?]
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:536) [MinecraftServer.class:?]
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_91]
Caused by: java.lang.IllegalStateException: Entity is already tracked!
    at net.minecraft.entity.EntityTracker.addEntityToTracker(EntityTracker.java:217) ~[EntityTracker.class:?]
    ... 21 more