GitLab runner not able to fetch AWS ECR images in the current AWS account GitLab and GitLab runners are running on the same host (I know how bad it is). There is an IAM Role attached to the EC2 on which GitLab is running.

This IAM Role gives the permission to perform some actions on multi-account ECR's.

Runners use docker as executor and assume role perfectly to push,pull images.
But, if images need to be pulled/pushed to the account on which GitLab is running, it doesn't work. I first need to pull images on the GitLab host so they are accessible within the runners.

I did a small test: I manually started a container directly on the GitLab host and ran aws ecr get-login... and I was able to login on the account.

I've installed amazon-ecr-credential-helper and configured like stated in the doc.

I don't understand why runners cannot pull images from the account...
I use this script in gitlab-ci.yml

image: docker:19.03
services:
- docker:19.03.0-dind
before_script:
- $(aws ecr get-login --no-include-email --region eu-central-1)


... and provide AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY variables into Settings/CI-CD section. 
Ensure your region with images is the same where are you logging in.