CPU is almost in every hour at 100%, how to reduce?

Hello.

Please check the EC2 system log by following the steps in the document below.
I think there is probably an error message being output that is causing the issue.
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/troubleshoot-unreachable-instance.html#instance-console-console-output

By the way, are you hosting any applications on that EC2?
If it is hosted, that application may be the cause.