Healthd service not sending data to ElasticBeanstalk

Hi, I'm deploying an app on tomcat8 on 2 t3.micro instances hosted both on a private subnets with NAT access to 2 public subnets, and registred as targets on an Application loadbalancer. My environment works well except that it doesn't receive data from the instances for the enhanced health check.

I've checked /var/log/healthd/daemon.log and find this error Aws::Errors::MissingCredentialsError) unable to sign request without credentials set. Backing off by 200 seconds in addition to delay interval as a Warning

when I was assigning public IP addresses to my instances and a classic loadbalancer the health checks pass but now it doesn't.

Is there another config to add in order to make it work ? Thanks