Problem/Bug Minecraft Crash Report

my minecraft server crash i'm french so sorry for my bad English

Okey the list of details of my crash report

what is the probleme

Code:

---- Minecraft Crash Report ----
// Uh... Did I do that?
Time: 3/29/17 4:04 PM
Description: Exception ticking world
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_8_R1.World.a(World.java:2325)
 at net.minecraft.server.v1_8_R1.SpawnerCreature.a(SpawnerCreature.java:94)
 at net.minecraft.server.v1_8_R1.WorldServer.doTick(WorldServer.java:213)
 at net.minecraft.server.v1_8_R1.MinecraftServer.z(MinecraftServer.java:707)
 at net.minecraft.server.v1_8_R1.DedicatedServer.z(DedicatedServer.java:284)
 at net.minecraft.server.v1_8_R1.MinecraftServer.y(MinecraftServer.java:609)
 at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:517)
 at java.lang.Thread.run(Thread.java:745)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------
-- Head --
Stacktrace:
 at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
 at java.util.ArrayList$Itr.next(ArrayList.java:851)
 at net.minecraft.server.v1_8_R1.World.a(World.java:2325)
 at net.minecraft.server.v1_8_R1.SpawnerCreature.a(SpawnerCreature.java:94)
 at net.minecraft.server.v1_8_R1.WorldServer.doTick(WorldServer.java:213)
-- Affected level --
Details:
 Level name: Factions
 All players: 11 total; [EntityPlayer['Xwiner_PvP'/12581, l='Factions', x=-3694.96, y=6.73, z=1283.00](Xwiner_PvP at -3694.956966839353,6.728933602796826,1283.001077345051), EntityPlayer['AdvenLokie'/13599, l='Factions', x=8.68, y=86.00, z=-16.05](AdvenLokie at 8.680522172805233,86.0,-16.05408166040047), EntityPlayer['ThomCraft_YT'/26966, l='Factions', x=4915.89, y=245.00, z=150.46](ThomCraft_YT at 4915.891731990092,245.0,150.4590036330578), EntityPlayer['YaNnPvP65'/77948, l='Factions', x=-3697.57, y=6.80, z=1279.76](YaNnPvP65 at -3697.5651329954258,6.804408283906599,1279.763343118892), EntityPlayer['dimitri7483'/107662, l='Factions', x=-3698.58, y=5.00, z=1282.91](dimitri7483 at -3698.576652851726,5.0,1282.9131577360233), EntityPlayer['BoBTheBriicoleur'/397015, l='Factions', x=-4925.78, y=6.00, z=1190.26](BoBTheBriicoleur at -4925.783576423141,6.0,1190.2604209073256), EntityPlayer['DarkHeroes'/13822, l='Factions', x=-22.68, y=68.00, z=20.81](DarkHeroes at -22.677629757416334,68.0,20.807934903022417), EntityPlayer['max2002'/13839, l='Factions', x=-3692.11, y=5.00, z=1281.38](max2002 at -3692.1119796072644,5.0,1281.384619702102), EntityPlayer['ItsFight_'/86173, l='Factions', x=428.50, y=5.00, z=-662.50](ItsFight_ at 428.5,5.0,-662.5), EntityPlayer['silvers123'/17916, l='Factions', x=-23.91, y=68.00, z=21.20](silvers123 at -23.906258721582166,68.0,21.20056025057967), EntityPlayer['Nonky9_'/1804, l='Factions', x=-3696.31, y=5.00, z=1282.34](Nonky9_ at -3696.3074091579483,5.0,1282.336527221803)]
 Chunk stats: ServerChunkCache: 1510 Drop: 0
 Level seed: 7532893272942520203
 Level generator: ID 00 - default, ver 1. Features enabled: true
 Level generator options: 
 Level spawn location: 8.00,88.00,-8.00 - World: (8,88,-8), Chunk: (at 8,5,8 in 0,-1; contains blocks 0,0,-16 to 15,255,-1), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,0,-512 to 511,255,-1)
 Level time: 167561589 game time, 168715640 day time
 Level dimension: 0
 Level storage version: 0x04ABD - Anvil
 Level weather: Rain time: 34904 (now: false), thunder time: 6557 (now: false)
 Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
 at net.minecraft.server.v1_8_R1.MinecraftServer.z(MinecraftServer.java:707)
 at net.minecraft.server.v1_8_R1.DedicatedServer.z(DedicatedServer.java:284)
 at net.minecraft.server.v1_8_R1.MinecraftServer.y(MinecraftServer.java:609)
 at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:517)
 at java.lang.Thread.run(Thread.java:745)
-- System Details --
Details:
 Minecraft Version: 1.8
 Operating System: Linux (amd64) version 3.14.32-xxxx-std-ipv6-64-hz1000
 Java Version: 1.8.0_112, Oracle Corporation
 Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
 Memory: 502569304 bytes (479 MB) / 1699262464 bytes (1620 MB) up to 6227755008 bytes (5939 MB)
 JVM Flags: 20 total; -Xincgc -XX:+UseParNewGC -XX:MaxPermSize=256M -XX:NewRatio=2 -XX:CMSFullGCsBeforeCompaction=1 -XX:+UseConcMarkSweepGC -XX:SoftRefLRUPolicyMSPerMB=2048 -XX:+CMSParallelRemarkEnabled -XX:+DisableExplicitGC -Xnoclassgc -Xoss4M -Xss4M -XX:+UseFastAccessorMethods -XX:CMSInitiatingOccupancyFraction=90 -XX:UseSSE=4 -XX:+UseCMSCompactAtFullCollection -XX:ParallelGCThreads=4 -XX:+AggressiveOpts -Xmx6144M -Xms512M
 IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
 CraftBukkit Information: 
  Running: CraftBukkit version git-Bukkit-33d5de3 (MC: 1.8) (Implementing API version 1.8-R0.1-SNAPSHOT) false

 

Why are you still on 1.8? Please read this thread.

 

I'm still on 1.8 beacause With Via version For 1.9 my server crash more times