A company hosts a highly available, scalable, and resilient application on Amazon EC2 instances that are part of an Auto Scaling group. A network engineer is planning to integrate IPv6 support with the application deployment in phases. The first phase is to enable IPv6 service consumption on the public Network Load Balancers (NLBs) that are deployed across the infrastructure. The target groups for the NLBS are configured as the Auto Scaling groups of the EC2 instances that host the application. The NLBs are configured for dual-stack operation.

During the testing of the first phase, the IPv6 application queries are not reaching the backend servers.

What is the cause of this issue?