DNS resolution fails for Windows Server container running in AWS ECS

Question

I have a C# web service running in a Windows Server ECS container (Fargate) in AWS. The container uses awsvpc network mode and has a load balancer. The web service is attempting to make an HTTP call to https://custom-domain-name.com/ but gets an error saying DNS name does not exist. This domain is hosted in an external cloud provider in a different country.

Using the AWS CLI and connecting to the ECS container I can verify the DNS for google.com and other domains using Powershell. I have verified the https://custom-domain-name.com/ domain on https://dnschecker.org/. That is, the domain is correctly registered. However attempting to run:

Resolve-DnsName custom-domain-name.com

produces the same error: DNS name does not exist. The web service successfully makes HTTP calls to 4 other URLs. These URLs resolve to other web services running in AWS ECS. If I run:

nslookup custom-domain-name.com 8.8.8.8

it succeeds. That is, the domain name is successfully resolved when using Google's DNS servers.

I can connect to https://custom-domain-name.com/ both from my browser as well as a C# application running on my PC. DNS resolution is enabled in our VPC (Virtual Private Cloud) instance in AWS. All the respective subnets in our VPC appear to have been correctly configured. There is a default wildcard rule that blocks internet traffic (0.0.0.0/0) on the Network ACL, however there is another rule that allows this. I am assuming this overrides the wildcard.