Fix EC2 Reachability Check Failure

My Ubuntu-based EC2 instance refuses to pass the second status check: AWS reports “Instance reachability check failed.” The box shows 1/2 checks passed, so it never becomes reachable by SSH. I use several custom configurations, so I’m leaning toward an OS-level boot problem rather than volume-mount or resource exhaustion.

Here’s what I need:
• Pinpoint the exact reason the reachability check is failing (likely boot sequence or kernel).
• Apply the fastest, cleanest fix so the instance launches normally and data stays intact.
• Document the steps you take and any commands or AMI snapshots you create so I can reproduce the recovery if it resurfaces.

You’ll probably work with the AWS Console, System Logs, EC2 Serial Console, and possibly create a rescue instance to mount the root volume, patch fstab, review cloud-init logs, or roll back a mis-configured kernel—whatever gets it booting again.

Success is the instance passing both status checks and being SSH-accessible with all existing data and services operating as before.