EC2 Instance became unresponsive and SSH failed until restart

Our EC2 instance (US-West-2) became unresponsive, web traffic failed to connect, and I could not SSH into the server.

After shutting down and then launching the instance again activity and access have returned to normal, but I would like to know the cause so this doesn't happen again in the future.

I have checked the syslog files but there was nothing obvious logged that would have caused the issue

Any advice would be much appreciated

The instance_id: i-0d2dc06a6d078f519

The instance type is: c5a.2xlarge