[Vanilla 1.12.2] "Exception ticking world" causes crash every 2 hours

Hey there!

I've set up a dedicated server under linux to run a Minecraft 1.12.2 server.
Everything works except that it now shuts down almost every 2 hours.

Exception description: "Exception ticking world"
Exception thrown: java.util.ConcurrentModificationException

I hope this helps resolving the bug

Greetings,
Jannik Neumann

crash-report as follows:

---- Minecraft Crash Report ----
// Shall we play a game?

Time: 29.06.18, 21:13
Description: Exception ticking world

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.remove(java.base@9-internal/HashMap.java:1503)
	at on.d(SourceFile:198)
	at oo.d(SourceFile:206)
	at net.minecraft.server.MinecraftServer.D(SourceFile:624)
	at nz.D(SourceFile:349)
	at net.minecraft.server.MinecraftServer.C(SourceFile:560)
	at net.minecraft.server.MinecraftServer.run(SourceFile:464)
	at java.lang.Thread.run(java.base@9-internal/Thread.java:804)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Server thread
Stacktrace:
	at java.util.HashMap$HashIterator.remove(java.base@9-internal/HashMap.java:1503)
	at on.d(SourceFile:198)
	at oo.d(SourceFile:206)

-- Affected level --
Details:
	Level name: world
	All players: 0 total; []
	Chunk stats: ServerChunkCache: 570 Drop: 299
	Level seed: -7030951689134580494
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: 
	Level spawn location: World: (-252,64,-56), Chunk: (at 4,4,8 in -16,-4; contains blocks -256,0,-64 to -241,255,-49), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
	Level time: 10738775 game time, 10895659 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 15454 (now: true), thunder time: 57845 (now: false)
	Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
	at net.minecraft.server.MinecraftServer.D(SourceFile:624)
	at nz.D(SourceFile:349)
	at net.minecraft.server.MinecraftServer.C(SourceFile:560)
	at net.minecraft.server.MinecraftServer.run(SourceFile:464)
	at java.lang.Thread.run(java.base@9-internal/Thread.java:804)

-- System Details --
Details:
	Minecraft Version: 1.12.2
	Operating System: Linux (amd64) version 4.4.0-042stab130.1
	Java Version: 9-internal, Oracle Corporation
	Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 80434712 bytes (76 MB) / 489684992 bytes (467 MB) up to 1073741824 bytes (1024 MB)
	JVM Flags: 1 total; -Xmx1024M
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Profiler Position: N/A (disabled)
	Player Count: 0 / 12; []
	Is Modded: Unknown (can't tell)
	Type: Dedicated Server (map_server.txt)