A team enabled Amazon VPC access on an AWS CodeBuild project so that integration tests could reach a private Amazon RDS database. The tests now connect to the database successfully, but every build fails later: docker pull from Amazon ECR times out, aws s3 cp of the build artifact times out, and installing public npm packages times out. The project is configured with two public subnets that have a default route to an internet gateway, and the build security group allows all outbound traffic and has no inbound rules.
What is the most likely cause, and what should the team change?