The issue that is occurring is the following;
I was given an ssh key (specifically a .ppk file for an AWS server). When I try to use the key through shell, I get prompted for a password; i.e.
ssh -i ~/.ssh/*ssh_key*.ppk *user*@*hostname*
However, when I use a client such as Filezilla, I am able to simply specify the keyfile during authentication configuration and the client will connect without issues. There is not prompt for authenticating against the keyfile.
This only happens with this one key, I've never had an issue like this before with other ssh keys.
I am on Ubuntu 16.04.5 LTS - kernal 4.15.0.36 #39