To disable debug mode on HassOS (instructions on enabling it can be found here), delete the file at /root/.ssh/authorized_keys and reboot:
$ ssh root@hassio.local -p 22222
_ _ _ _ _
| | | | /\ (_) | | | |
| |__| | ___ _ __ ___ ___ / \ ___ ___ _ ___| |_ __ _ _ __ | |_
| __ |/ _ \| '_ ` _ \ / _ \ / /\ \ / __/ __| / __| __/ _` | '_ \| __|
| | | | (_) | | | | | | __/ / ____ \\__ \__ \ \__ \ || (_| | | | | |_
|_| |_|\___/|_| |_| |_|\___| /_/ \_\___/___/_|___/\__\__,_|_| |_|\__|
Welcome on Home Assistant command line.
For more details use 'help' and 'exit' to close.
If you need access to host system use 'login'.
ha > login
# rm /root/.ssh/authorized_keys
# reboot