[14:49:32] [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:809) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:405) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:678) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:576) [spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_112]
Caused by: java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) ~[?:1.8.0_112]
	at java.util.ArrayList$Itr.next(ArrayList.java:851) ~[?:1.8.0_112]
	at net.minecraft.server.v1_12_R1.World.a(World.java:2547) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.SpawnerCreature.a(SpawnerCreature.java:122) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.WorldServer.doTick(WorldServer.java:286) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:798) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	... 4 more
[14:49:32] [Server thread/ERROR]: 	Cause of unexpected exception was
java.util.ConcurrentModificationException: null
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) ~[?:1.8.0_112]
	at java.util.ArrayList$Itr.next(ArrayList.java:851) ~[?:1.8.0_112]
	at net.minecraft.server.v1_12_R1.World.a(World.java:2547) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.SpawnerCreature.a(SpawnerCreature.java:122) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.WorldServer.doTick(WorldServer.java:286) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:798) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:405) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:678) ~[spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:576) [spigot-1.12.jar:git-Spigot-596221b-2c5c611]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_112]
[14:49:32] [Server thread/ERROR]: This crash report has been saved to: /home/gs/gs/data/servers/5699522/./crash-reports/crash-2017-07-30_14.49.32-server.txt