18W11A: Server Exception in ticking world while trying to log on

UNMODDED: USING VANILLA: (similar bug was not found in my searches)
using existing 1.12.2 world and new 18w11a server.jar, runserver :
"C:\Program Files\Java\jre1.8.0_161\bin\java.exe" -server -Xmx3192M -Xms3192M -XX:-UseConcMarkSweepGC -XX:+ScavengeBeforeFullGC -XX:-UseParallelGC -XX:ParallelGCThreads=2 -jar server.jar nogui

was able to play for 1/2 hour but when I tried to log back in:(please see attached crash report)
[21:39:45] [Server thread/INFO]: cyrixlord joined the game
[21:39:46] [Server thread/ERROR]: Encountered an unexpected exception
h: Exception ticking world
at net.minecraft.server.MinecraftServer.w(SourceFile:698) ~[server.jar:?]
at rp.w(SourceFile:354) ~[server.jar:?]
at net.minecraft.server.MinecraftServer.v(SourceFile:627) ~[server.jar:?]
at net.minecraft.server.MinecraftServer.run(SourceFile:532) [server.jar:?]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_161]
Caused by: i: Non [a-z0-9/._-] character in path of location: minecraft:Zombie