mongo db project

Hi, I'm running a MongoDB replica set (PSA). All nodes are running on different machines. Everything was fine until yesterday. I have made two big migrations. 1st clean some fields in collections that I no longer need. 2nd update a huge collection with a new field. After the migrations, the migration process took nearly 30seconds and secondary stopped working (Hits %100 CPU) and I don't know what is happening. It seems it's working but something is really odd. The primary node is also working with %80 CPU. In general, it's %20-30 so it seems there is a problem on the primary node too. The application is running smoothly. I need some help to solve my problem. First of all the application is running and customers are using it so there isn't an option to stop the primary node. Secondly here what I want from the winner: - The replica set is not working properly the awarded developer must provide it to run correctly. - I started them with commands all nodes must work as a service. After reboot, they must start automatically. - The authentication and security of the setup should be checked.