Gitlab CI Reports Preparation failed: Error: No such image even though image exists

Description of the problem

Some images in Docker registry cannot be found, reporting Error: no such image even though they show up under the Registry Section of the project. Error output:

Pulling docker image registry.gitlab.com/gitschooldude/hello/centos6:latest ...
ERROR: Preparation failed: Error: No such image: registry.gitlab.com/gitschooldude/hello/centos6:latest (executor_docker.go:175:0s)
Will be retried in 3s ...

The gitlab-ci.yml file specifies the image registry.gitlab.com/gitschooldude/hello/centos6:latest for all jobs. But all jobs will fail with the above error, one such example. However, if I change this image to be registry.gitlab.com/gitschooldude/hello/ubuntu:latest the ubuntu docker image is pulled no problem. Both of these images are defined in the project registry so I don't understand why one works and the other reports No such image

Which Group/Project (with full path) is experiencing the issue?

https://gitlab.com/gitschooldude/hello/

Approximate date/time when the error occurred.

Within the last two hours of posting this issue, 2PM CST March 2nd 2019

Describe what you were doing right before the issue occurred.

I pushed an updated version of my centos6:latest docker image, moving to newer image id be48122ed0b1 which simply added a couple packages xclock and gvim. Here's a pipeline that worked right before I updated the image in the registry producing no issues.

In attempting to debug/fix this I tried various image naming schemes and removed and re-pushed all images, that didn't help. I have also tried centos7:latest and have the same problem. I'm stuck, please help!