When running a summon command such as {{/summon bat, }}when this is prevented by a plugin that cancels the CreatureSpawnEvent, the following error message is printed in chat:

"Unable to summon entity due to duplicate UUIDs"

This is extremely confusing as it has nothing to do with UUIDs whatsoever.

Instead it should print a message that indicates that spawning was prevented by spigot/plugin/[name of plugin].

Plugins that trigger this issue:

• Multiverse-core (configure the dimension to disallow animal & mob spawning)
• HungerGames (create a hungergames region, inside mob spawning is prevented)