This looks like its an issue with the nextclient implemented on
kiwiirc.org.
It started 09/25/2022 shortly after 8pm UTC.
Trying to connect to my own public VPS IRC node with packet capture showed no packets were traversing inbound from Kiwi.
I confirmed with Libera.chat that the issue is not on their side. Some people at libera tested five other commonly used irc servers from Kiwi and received the same error.
Kiwi IRC might want to look into what's going on with their infrastructure and change the error to something less misleading to the end-user.
The error I received made it appear the user was banned.
Best Regards
N.