In Debian a lot of times SSH disables the root user to login by password by default. This means you will get an authentication failure as if you typed in the wrong password.
The logs also indicate the password is wrong but what is often the case is in the config file
Check /etc/ssh/sshd_config
cat /etc/ssh/sshd_config|grep -i permitrootlogin
Make sure it says:
PermitRootLogin yes
If not change it and restart SSH and it will work again.
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