[01:49:46] [Server thread/ERROR]: Encountered an unexpected exception
net.minecraft.server.v1_12_R1.ReportedException: Exception ticking world
	at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:812) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:406) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:679) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:577) [spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_131]
Caused by: java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) ~[?:1.8.0_131]
	at java.util.ArrayList$Itr.next(ArrayList.java:851) ~[?:1.8.0_131]
	at net.minecraft.server.v1_12_R1.World.a(World.java:2550) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.SpawnerCreature.a(SpawnerCreature.java:122) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.WorldServer.doTick(WorldServer.java:286) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:801) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	... 4 more
[01:49:46] [Server thread/ERROR]: 	Cause of unexpected exception was
java.util.ConcurrentModificationException: null
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) ~[?:1.8.0_131]
	at java.util.ArrayList$Itr.next(ArrayList.java:851) ~[?:1.8.0_131]
	at net.minecraft.server.v1_12_R1.World.a(World.java:2550) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.SpawnerCreature.a(SpawnerCreature.java:122) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.WorldServer.doTick(WorldServer.java:286) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:801) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:406) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:679) ~[spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:577) [spigot-1.12.1.jar:git-Spigot-65e8124-963b19c]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_131]
[01:49:46] [Server thread/ERROR]: This crash report has been saved to