The //regen command in WorldEdit throws up an error and when I contacted the WorldEdit guys they told me it was due to a bug in Spigot as it uses World#regenerateChunk. Searching on Jira I found a bug report for 1.13 where it got fixed.

https://hub.spigotmc.org/jira/browse/SPIGOT-4137

Tested both on a local running server and the one hosted at a datacenter. Both do nothing in game when using //regen and both throw the same error.

I also use plotsquared which produces the same error.

// code placeholder

[12:58:01] [Server thread/WARN]: Chunk generation via Bukkit raised an error[12:58:01] [Server thread/WARN]: Chunk generation via Bukkit raised an errorjava.lang.UnsupportedOperationException: Not supported in this Minecraft version! Unless you can fix it, this is not a bug at org.bukkit.craftbukkit.v1_14_R1.CraftWorld.regenerateChunk(CraftWorld.java:400) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at com.sk89q.worldedit.bukkit.BukkitWorld.regenerate(BukkitWorld.java:182) ~[?:?] at com.sk89q.worldedit.command.RegionCommands.regenerateChunk(RegionCommands.java:367) ~[?:?] at com.sk89q.worldedit.command.RegionCommandsRegistration._regen(RegionCommandsRegistration.java:560) ~[?:?] at org.enginehub.piston.CommandManager.execute(CommandManager.java:159) ~[?:?] at com.sk89q.worldedit.extension.platform.PlatformCommandManager.handleCommand(PlatformCommandManager.java:460) ~[?:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_181] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181] at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181] at com.sk89q.worldedit.util.eventbus.MethodEventHandler.dispatch(MethodEventHandler.java:58) ~[?:?] at com.sk89q.worldedit.util.eventbus.EventHandler.handleEvent(EventHandler.java:73) ~[?:?] at com.sk89q.worldedit.util.eventbus.EventBus.dispatch(EventBus.java:187) ~[?:?] at com.sk89q.worldedit.util.eventbus.EventBus.post(EventBus.java:173) ~[?:?] at com.sk89q.worldedit.bukkit.WorldEditPlugin.onCommand(WorldEditPlugin.java:304) ~[?:?] at com.sk89q.bukkit.util.DynamicPluginCommand.execute(DynamicPluginCommand.java:55) ~[?:?] at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:149) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at org.bukkit.craftbukkit.v1_14_R1.CraftServer.dispatchCommand(CraftServer.java:707) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.PlayerConnection.handleCommand(PlayerConnection.java:1666) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.PlayerConnection.a(PlayerConnection.java:1506) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.PacketPlayInChat.a(PacketPlayInChat.java:47) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.PacketPlayInChat.a(PacketPlayInChat.java:1) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:13) ~[spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.TickTask.run(SourceFile:18) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.executeTask(SourceFile:135) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.executeNext(SourceFile:114) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.MinecraftServer.aW(MinecraftServer.java:896) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.MinecraftServer.executeNext(MinecraftServer.java:889) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.IAsyncTaskHandler.awaitTasks(SourceFile:123) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.MinecraftServer.sleepForTick(MinecraftServer.java:873) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at net.minecraft.server.v1_14_R1.MinecraftServer.run(MinecraftServer.java:806) [spigot-1.14.jar:git-Spigot-1eece4f-0d76f86] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_181]