[MC-101155] Crashes when opening my redstone world or joining the server

What I expected to happen was...:
i was just opening my redstone world and later joining the server

What actually happened was...:
it loaded up and after 2/3 secs it crashes

Steps to Reproduce:
1. load the world
2. wait few seconds
3. instant crash

Client

Description: Batching chunks

java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
	at java.util.ArrayList$Itr.remove(Unknown Source)
	at aht.a(SourceFile:1861)
	at ase.a(SourceFile:634)
	at aic.r(SourceFile:63)
	at bqb.b(SourceFile:160)
	at bpx.a(SourceFile:100)
	at bpx.run(SourceFile:43)
	at java.lang.Thread.run(Unknown Source)

Server

Description: Exception ticking world

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.remove(Unknown Source)
	at lp.d(SourceFile:198)
	at lq.d(SourceFile:201)
	at net.minecraft.server.MinecraftServer.D(SourceFile:618)
	at net.minecraft.server.MinecraftServer.C(SourceFile:554)
	at byk.C(SourceFile:155)
	at net.minecraft.server.MinecraftServer.run(SourceFile:458)
	at java.lang.Thread.run(Unknown Source)