Hi @Jihoon_Shim - Firstly, welcome to the community.
Why MongoDB Automation Agent suddenly connects to our server so much ?
Please contact the Atlas support team via the in-app chat to investigate any operational and billing issues related to your Atlas account as the support team would have more insight into the cluster in question if you are certain that the automation agent is causing the connect spikes. You can additionally raise a support case if you have a support subscription. You could possibly investigate the Project Activity Feed as well during those same time frames of when the spikes occurred to see if any particular cluster maintenance tasks were happening.
Regards,
Jason