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This looks more like a cacheing issue though. You can try running a rebuild and restart, that should reset the cache buster.
Basically, we just had a guy have an outburst and then delete their own account. How do I prevent this person from registering again? I can't find their username anymore in the Users dashboard, so I can't ban them.
Is there a way to ban an IP without an associated user? And, is there a way to delete specific guest posts associated with that IP without manually deleting them all?
Check out the event lot page in the ACP (under advanced). The user's deletion event should have been logged, and the IP address should have been saved.
... as long as your NodeBB is new enough, that is