I'm sorry I can't think of a more descriptive title. I have a consistent crash in the same location for a given seed. I've not been able to even guess as to why in order to reproduce on other maps and I've yet to run into elsewhere. Below is the bug report.

Steps to reproduce:
Generate normal world with seed: 4588975552582455796
Creative mode, bonus box=true
TP your player to -5800 100 -3800
Fly/float west in creative.
It crashes every time.

---- Minecraft Crash Report ----
// This is a token for 1 free hug. Redeem at your nearest Mojangsta: _HUG~

Time: 5/9/18 6:00 PM
Description: Exception generating new chunk

java.util.concurrent.ExecutionException: java.lang.RuntimeException: We are asking a region for a chunk out of bound | -774 -489
at java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)
at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1895)
at si.c(SourceFile:130)
at sq.a(SourceFile:84)
at sr.c(SourceFile:143)
at sj.i_(SourceFile:223)
at net.minecraft.server.MinecraftServer.w(SourceFile:689)
at net.minecraft.server.MinecraftServer.v(SourceFile:622)
at dhm.v(SourceFile:156)
at net.minecraft.server.MinecraftServer.run(SourceFile:527)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.RuntimeException: We are asking a region for a chunk out of bound | -774 -489
at so.c(SourceFile:115)
at bay.y(SourceFile:45)
at so.a_(SourceFile:121)
at bto.a(SourceFile:144)
at bto.a(SourceFile:16)
at bxn.a(SourceFile:20)
at bxn.a(SourceFile:13)
at brp.a(SourceFile:27)
at bbr.a(SourceFile:516)
at bpc.a(SourceFile:109)
at sx.a(SourceFile:12)
at sw.a(SourceFile:33)
at bpg.a(SourceFile:85)
at tc.a(SourceFile:59)
at tc.a(SourceFile:23)
at afz$a.a(SourceFile:143)
at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:602)
at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:577)
at java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:443)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
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:
---------------------------------------------------------------------------------------

– Head –
Thread: Server thread
Stacktrace:
at java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)

– Chunk to be generated –
Details:
Location: -385,-243
Position hash: -1039382086017
Generator: bqx@56d2e014
Stacktrace:
at si.a(SourceFile:180)
at si.c(SourceFile:133)
at sq.a(SourceFile:84)
at sr.c(SourceFile:143)
at sj.i_(SourceFile:223)
at net.minecraft.server.MinecraftServer.w(SourceFile:689)
at net.minecraft.server.MinecraftServer.v(SourceFile:622)
at dhm.v(SourceFile:156)
at net.minecraft.server.MinecraftServer.run(SourceFile:527)
at java.lang.Thread.run(Thread.java:745)

– Affected level –
Details:
Level name: Crashy
All players: 1 total; [sl['BrugesZot'/324, l='Crashy', x=-5931.91, y=113.11, z=-3884.18]]
Chunk stats: ServerChunkCache: 1098 Drop: 0
Level seed: 4588975552582455796
Level generator: ID 00 - default, ver 1. Features enabled: true
Level generator options: {}
Level spawn location: World: (-80,69,128), Chunk: (at 0,4,0 in -5,8; contains blocks -80,0,128 to -65,255,143), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 3244 game time, 3244 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 23634 (now: false), thunder time: 165321 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true

– System Details –
Details:
Minecraft Version: 18w19b
Operating System: Mac OS X (x86_64) version 10.13.4
Java Version: 1.8.0_74, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 1118952152 bytes (1067 MB) / 2583691264 bytes (2464 MB) up to 6442450944 bytes (6144 MB)
JVM Flags: 7 total; -Xmx6G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
Profiler Position: N/A (disabled)
Player Count: 1 / 8; [sl['BrugesZot'/324, l='Crashy', x=-5931.91, y=113.11, z=-3884.18]]
Data Packs: vanilla
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.