Description: Exception in server tick loop

java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
	at java.util.ArrayList$Itr.next(ArrayList.java:851)
	at net.minecraft.server.v1_11_R1.ServerConnection.c(ServerConnection.java:135)
	at net.minecraft.server.v1_11_R1.MinecraftServer.D(MinecraftServer.java:842)
	at net.minecraft.server.v1_11_R1.DedicatedServer.D(DedicatedServer.java:399)
	at net.minecraft.server.v1_11_R1.MinecraftServer.C(MinecraftServer.java:678)
	at net.minecraft.server.v1_11_R1.MinecraftServer.run(MinecraftServer.java:576)
	at java.lang.Thread.run(Thread.java:745)