crash-2019-05-05_12.29.12-server.txt
Hello again. Server crash when I try "confirm" the fill to 100% again. Minecraft version 1.14.
This server is running CraftBukkit version git-Spigot-1eece4f-84400e6 (MC: 1.14) (Implementing API version 1.14-R0.1-SNAPSHOT)

[13:03:05] [Server thread/INFO]: You are running the latest version.
More info?

No indication of anything in that stacktrace or entire crash report to do with WorldBorder.

The likely culprit is indicated in the stacktrace:
org.bukkit.plugin.IllegalPluginAccessException: Plugin attempted to register net.citizensnpcs.trait.Gravity@7c2c3272 while not enabled

So... it looks like the plugin "citizensnpcs" is disabled but for some reason still trying to register stuff. Whatever the case, again, nothing to do with this plugin.

just for confirm to let don't remove chunks which are important. I have to remove the plugin right?