SQS is not working for multiple ECS (fargate) instances

I am using an application load balancer, under this ALB, a target group is provided. In this target group, two fargate ECS instances are running. These two instances use the same PHP docker image. When i upload an csv file, the tasks in the csv file will be moved to the SQS. Here the tasks are not passing to the SQS and no error messages were showing.So i changed the ECS instance number to 1 ( initially it was 2) then SQS is working fine. So how do i resolve this issue for multiple ECS containers.