Server crashed when I have replaced server JAR file of 18w22c with 1.13-pre1 (without regenerating the world ! )
[19:24:06] [Server thread/INFO]: Wawua left the game
[19:24:06] [Server thread/WARN]: handleDisconnection() called twice
[19:24:06] [Server Shutdown Thread/INFO]: Saving worlds
[19:24:06] [Server Shutdown Thread/INFO]: Saving chunks for level 'world'/overworld
[19:24:07] [Server Shutdown Thread/ERROR]: Failed to save chunk
java.util.ConcurrentModificationException: null
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909) ~[?:1.8.0_172]
at java.util.ArrayList$Itr.next(ArrayList.java:859) ~[?:1.8.0_172]
at bbv.a(SourceFile:121) ~[server.1.13-pre1.jar:?]
at bbv.a(SourceFile:106) ~[server.1.13-pre1.jar:?]
at bbv.a(SourceFile:152) ~[server.1.13-pre1.jar:?]
at bqx.a(SourceFile:432) ~[server.1.13-pre1.jar:?]
at bqx.a(SourceFile:216) [server.1.13-pre1.jar:?]
at sl.b(SourceFile:217) [server.1.13-pre1.jar:?]
at sl.a(SourceFile:237) [server.1.13-pre1.jar:?]
at sm.a(SourceFile:737) [server.1.13-pre1.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:445) [server.1.13-pre1.jar:?]
at net.minecraft.server.MinecraftServer.h_(SourceFile:470) [server.1.13-pre1.jar:?]
at net.minecraft.server.MinecraftServer$2.run(SourceFile:814) [server.1.13-pre1.jar:?]
[19:24:08] [Server Shutdown Thread/INFO]: Saving chunks for level 'world'/the_nether
This is a reset caused by server watchdog.
Please attach the server.log from the time immediately before the watchdog.