Crash when quickly generating new terrain while world is still loading

I got a similar crash with 18w07a. (We're using 18w07a because 18w07b and 18w07c clients crash for multiplayer). A user on my test server said he did something that gave him a massive amount of speed, and that's when it crashed. In my attachment, first you'll find the crash report, followed by the relevant section of the log file.

I have a similar crash in 18w15a when loading a superflat test world with only a few different blocks. This test world was created in 1.12.2. World is attached as "x112113crash.zip".

Crash log:

Minecraft Crash Report ----
// There are four lights!

Time: 16/04/18 4:43 PM
Description: Exception in server tick loop

java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: 827
at net.minecraft.server.MinecraftServer.i_(SourceFile:394)
at dal.a(SourceFile:115)
at dal.d(SourceFile:131)
at net.minecraft.server.MinecraftServer.run(SourceFile:502)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: 827
at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2272)
at net.minecraft.server.MinecraftServer.i_(SourceFile:392)
... 4 more
Caused by: java.lang.ArrayIndexOutOfBoundsException: 827
at it.unimi.dsi.fastutil.longs.Long2LongLinkedOpenHashMap$MapIterator.nextEntry(Long2LongLinkedOpenHashMap.java:1207)
at it.unimi.dsi.fastutil.longs.Long2LongLinkedOpenHashMap$EntryIterator.next(Long2LongLinkedOpenHashMap.java:1299)
at it.unimi.dsi.fastutil.longs.Long2LongLinkedOpenHashMap$EntryIterator.next(Long2LongLinkedOpenHashMap.java:1288)
at aum.a(SourceFile:25)
at aum.get(SourceFile:49)
at it.unimi.dsi.fastutil.longs.AbstractLong2ObjectFunction.get(AbstractLong2ObjectFunction.java:148)
at java.util.Map.computeIfAbsent(Map.java:955)
at sz.a(SourceFile:42)
at sz.a(SourceFile:23)
at zx.c(SourceFile:102)
at sg.d(SourceFile:153)
at bor.a(SourceFile:231)
at bor.a(SourceFile:80)
at bqv.a(SourceFile:16)
at bqv.a(SourceFile:13)
at bkw.a(SourceFile:27)
at avl.a(SourceFile:479)
at bjy.a(SourceFile:143)
at su.a(SourceFile:12)
at st.a(SourceFile:33)
at biq.a(SourceFile:85)
at sz.a(SourceFile:54)
at sz.a(SourceFile:23)
at zx$a.a(SourceFile:143)
at zx$a$$Lambda$900/6329757.apply(Unknown Source)
at java.util.concurrent.CompletableFuture$AsyncApply.exec(CompletableFuture.java:501)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:902)
at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1689)
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1644)
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

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

– System Details –
Details:
Minecraft Version: 18w15a
Operating System: Windows 7 (x86) version 6.1
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 70084416 bytes (66 MB) / 199000064 bytes (189 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
Profiler Position: N/A (disabled)
Player Count: 0 / 8; []
Data Packs: vanilla
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

Can anyone reproduce this issue in 1.13-pre5 or newer? (It seems tied pretty closely to MC-125807 to me, and that should no longer be happening with the JVM update).

Please check if that's still an issue in the latest 1.13 release or the latest 1.14 development snapshot.