[20:32:16 FATAL]: Error executing task
java.util.concurrent.ExecutionException: net.minecraft.server.v1_8_R3.ReportedException: Ticking player
        at java.util.concurrent.FutureTask.report(Unknown Source) ~[?:1.8.0_171]
        at java.util.concurrent.FutureTask.get(Unknown Source) ~[?:1.8.0_171]
        at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:45) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.MinecraftServer.lambda$startTickloop$1(MinecraftServer.java:598) ~[spigot.jar:1.8.8]
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_171]
        at java.util.concurrent.FutureTask.runAndReset(Unknown Source) [?:1.8.0_171]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(Unknown Source) [?:1.8.0_171]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) [?:1.8.0_171]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.8.0_171]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.8.0_171]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_171]
Caused by: net.minecraft.server.v1_8_R3.ReportedException: Ticking player
        at net.minecraft.server.v1_8_R3.EntityPlayer.l(EntityPlayer.java:374) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:369) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PacketPlayInFlying.a(PacketPlayInFlying.java:30) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PacketPlayInFlying$PacketPlayInPositionLook.a(PacketPlayInFlying.java:123) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PlayerConnectionUtils.lambda$ensureMainThread$0(PlayerConnectionUtils.java:6) ~[spigot.jar:1.8.8]
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_171]
        at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_171]
        at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) ~[spigot.jar:1.8.8]
        ... 8 more
Caused by: java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextNode(Unknown Source) ~[?:1.8.0_171]
        at java.util.HashMap$KeyIterator.next(Unknown Source) ~[?:1.8.0_171]
        at net.minecraft.server.v1_8_R3.EntityLiving.bi(EntityLiving.java:483) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.EntityLiving.K(EntityLiving.java:269) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.Entity.t_(Entity.java:261) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.EntityLiving.t_(EntityLiving.java:1489) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.EntityHuman.t_(EntityHuman.java:176) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.EntityPlayer.l(EntityPlayer.java:309) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:369) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PacketPlayInFlying.a(PacketPlayInFlying.java:30) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PacketPlayInFlying$PacketPlayInPositionLook.a(PacketPlayInFlying.java:123) ~[spigot.jar:1.8.8]
        at net.minecraft.server.v1_8_R3.PlayerConnectionUtils.lambda$ensureMainThread$0(PlayerConnectionUtils.java:6) ~[spigot.jar:1.8.8]
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_171]
        at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_171]
        at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) ~[spigot.jar:1.8.8]
        ... 8 more