SSH suddenly stopped working | Instance is healthy and passed status checks

SSH to my ubuntu t3a.small instance stopped working suddenly. I have tries following

1. SSH from putty using key pair. It was working before but stopped working today.
2. Connect using aws console instance connect.
3. I have verified that port 22 is open. vpc is attached to an internet gateway. I have made no chanhe to any network

This happen whenever I am running a npm run build recently. It will just hang instance. I checked remaining credit balance and it is 576 and cpu utlization is ~76%. This has happened very frequently recently. I have to restart my instance few times and then wait for ~30-40 minutes before I can ssh again.