Alright, here's a fun one.. I was trying to log into a headless debian server (rented VPS) of mine which I hadn't used for a while. I have two accounts pre-saved in Putty both with RSA key authentication.

When I went to log in, I got this...and it stayed at this indefinitely:

Using username "root".
Authenticating with public key "imported-openssh-key"

(This happens with more than the root account, and yes, I also have root ssh enabled in the config.)

As they both hang at the "Authenticating" message, I rebooted the VPS thinking it might've bogged down, but it didn't help. I did, however, find another account I made will login fine with either password or private key.

I tried removing authorized_keys from .ssh and then re-adding it by creating a new one with nano, but that didn't help either.

It's also not the key because I've used the same key for the account that works as I did for the others.

I'm at a loss as to what is broke, but I need to get it working again so I can deploy access to a third-party. Is anyone familiar as to why ssh key authentication can just entirely hang at the auth stage?

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EDIT:

I also found that if I change anything in the public key on the server, it will respond to an authentication request saying the server denied the key. But when fixing the public key, it goes back to hanging at the "Authenticating" message.