Instance reachability check failed

I am keep getting the "Instance reachability check failed".

During this time, we are unable to connect the instance using the APP or SSH. There is not much load to the application. Only few users are using the app and most of the times the CPU % is less than 5%. At times, it is also increasing it to 100% and coming down in few mins.

It is getting resolved automatically after 30+ mins or so. sometimes after reboot.

I don't see any issues in system logs.

May I know the reason for this abrupt behavior and the steps to resolve this issue? Appreciate your support!