I'm a bit stumped...

1) First account (the one I've been using) works perfectly fine on SSH and SFTP

2) Test account I created worked perfectly fine on SSH and SFTP

3) The other accounts do not work. When I attempt to login to the desired username, I get the following error:

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PuTTY Fatal Error
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Disconnected: No supported authentication methods available (server sent: publickey)
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OK
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Some details surrounding the issue:
I have the authorized_keys file containing the public key for each individual user in their respective /home/.ssh/ directories. The permissions match the structure of the 2 logins that work. Password authentication is disabled and none of the home directories are encrypted.

Hope someone on here can assist me! Thank you!

SOLVED

Thanks to Linode support for assisting me! The user's shell was improperly set somehow and in the process of troubleshooting I fussed a couple other things up. All good now!