Minecraft Cauldron Server Chat Error Despite OP?

I have a cauldron server (Bukkit, Spigot + Forge) with the following plugins:

-Worldedit -Worldguard -Multiverse (Core, Portals, Inventories) -EasyWarp -Essentials

If I write something in the chat, so no command like / say do, comes an Errormeldung: "Can't send chat message". It is not an Essentials or EasyWarp because this problem has already occurred before, as these plugins were not yet installed. I do not have mods yet, because I wanted to do the plugins first.

Believes in WorldGuard,

sometimes / rg info, maybe there's something weird in your area.

Unfortunately, everything is normal

Then take down WorldGuard and see if it's still there

Is still there.

Then take each plugins individually down and watch when it works