A banned player keeps knocking
What it looks like in your log
You are banned from this server.
What causes it
A banned account or IP tried to join and was refused. That is the ban working, not a fault.
How to fix it
If the ban was a mistake, lift it from the console with "pardon <name>" or "pardon-ip <address>". If you did not ban anyone, check banned-players.json and any ban plugin; shared ban lists sometimes arrive with a plugin.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log