[00:16:59] [Server thread/ERROR]: "Silently" catching entity tracking error.
net.minecraft.server.v1_10_R1.ReportedException: Adding entity to track
    at net.minecraft.server.v1_10_R1.EntityTracker.addEntity(EntityTracker.java:141) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.EntityTracker.track(EntityTracker.java:80) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.WorldManager.a(WorldManager.java:19) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.World.b(World.java:1028) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.WorldServer.b(WorldServer.java:1122) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.World.addEntity(World.java:1021) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:514) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:510) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:521) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.MobSpawnerAbstract.c(MobSpawnerAbstract.java:106) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.TileEntityMobSpawner.E_(SourceFile:90) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.World.tickEntities(World.java:1496) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.WorldServer.tickEntities(WorldServer.java:632) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.MinecraftServer.D(MinecraftServer.java:799) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:400) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:668) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:567) [Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_101]
Caused by: java.lang.IllegalStateException: Entity is already tracked!
    at net.minecraft.server.v1_10_R1.EntityTracker.addEntity(EntityTracker.java:108) ~[Spigot.jar:git-Spigot-e0e1771-5e5cf84]
    ... 17 more