Steps to reproduce:

1.- Create a new world  (like Hardcore or so).

2.- Set it to buffet type of world (It was desert in my case)

3.- Try to run it.

Crash report:

---- Minecraft Crash Report -------- Minecraft Crash Report ----// Hi. I'm Minecraft, and I'm a crashaholic.
Time: 28/03/19 10:39 AMDescription: Exception in server tick loop
n: Non [a-z0-9/._-] character in path of location: minecraft:cye$a$a@3437fc4f at qr.<init>(SourceFile:38) at qr.<init>(SourceFile:43) at bxs.m(SourceFile:100) at ve.a(SourceFile:164) at bgv.<init>(SourceFile:129) at ve.<init>(SourceFile:164) at net.minecraft.server.MinecraftServer.a(SourceFile:378) at dwo.a(SourceFile:82) at dwo.d(SourceFile:104) at net.minecraft.server.MinecraftServer.run(SourceFile:603) at java.lang.Thread.run(Unknown Source)

A detailed walkthrough of the error, its code path and all known details is as follows:---------------------------------------------------------------------------------------
– System Details --Details: Minecraft Version: 19w13a Operating System: Windows 10 (amd64) version 10.0 Java Version: 1.8.0_201, Oracle Corporation Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation Memory: 233665776 bytes (222 MB) / 624013312 bytes (595 MB) up to 1060372480 bytes (1011 MB) JVM Flags: 6 total; -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump 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.