Issues with ODK-Aggregate running in ECS Fargate behind AWS load balancer

I am running ODK-Aggregate behing AWS load balancer. ODK-Aggregate running in container as Fargate Service with just one container works fine. But as soon as I add one more container it randomly gives "Invalid Request" most of the times

I am using ODK-Aggregate as docker on ECS Fargate.

Playing with file

I think its not about AWS Load balancer. Just any load balancer running atleast two instances.

This is sample URL :
Try couple of options there. You will see a message with "Invalid Request"