EC2 instance kept randomly crashing

Hello,

My client's EC2 instance has been kept crashing randomly for a while, instance ID: i-0f4d7b0f00f614d62

When it went down, I couldn't ssh into it. I posted a question on serverfault: https://serverfault.com/questions/1127277/ec2-instance-randomly-crash

But some times it doesn't seem to be a memory issue, while I was monitoring memory usage, the system could suddenly go down even when it had sufficient memory at the last minute.

Could you investigate please?