EC2 no longer reachable via SSH or HTTP

I have an EC2 instance that is no longer reachable.
I was setting up a CAS (Central Authentication Server) Client for SSO. But was getting a Port Occupied error in the validation tests during the maven build.
So I was using lsof and ufw to check and open ports so see if I could fix it
I then moved to the EC2 Security Group tab in the console to see if the port was being blocked there.
After trying several things
I wondered if I had needed to restart the EC2 instance for the changes to take
and upon doing so, by rebooting from the console, the instance became unreachable.
I attempted to undo what I had done in the Security Group. But no luck and including a restart.
Since the EC2 had an ELB that it was registered to and some googling revealed that it might be the issue. I tried unregistering and reregistering the instance and just removing the instance from the ELB.

I have also tried the Amazon Support EC2 Resue SSM but that failed in execution