Undoubtedly the data would be lost when the 4G connection is down. Some local buffering on the RPi would be a great addition to this setup.
The load balancer is mainly for the ease of setting up https connections from the internet through it. That way, I don’t need to configure both InfluxDb and Grafana with certificates, a hassle of its own. Instead I can easily issue a certificate in AWS and connect it to the load balancer and then let the traffic between the load balancer and the ec2 instance go unsecured over http.