Continuously getting locked out from EC2 instance. No supported authentication methods available I am getting continously locked out from my ec2 instance time and again. I have to take its root volume and attach it to some other instance (mostly new instance) to prevent data loss. I am not able to figure out what is causing my ssh being denied. It works for sometime and all of a sudden ssh is denied. I have tried


Comparing the authkeys with my login key. It is same.
Copying the key from a ssh working instance to this volume and re-launching. Same error.
Did some tweaks in sshd_conf and ssh_conf but to no success.


I am completely stumped here, any viewpoints on this.
I have been working on AWS for sometime now and never encountered this problem, the only change being the organsation (and the network) has changed from where i am working from? Can their network be generated some kind of DOS attack which is just shutting down my ssh access? 
My team does not have an official AWS tech support plan, hence here.
Although i have not found out what leads to this. But i am finally able to login into my instance by following these steps:
1. As you are logged in create a user in the instance and give it a password.

$ adduser user1
$ passwd user1


2. Enable password authentication in /etc/sshd_config file.
3. Login with the new user.

Interestingly, this user does not gets locked out as the centos user.