Fresh install Gitlab Omnibus registry fails with 404 on docker push

I'm running gitlab on a fresh ubuntu 16.04 lightsail instance on AWS. I'm using letsencrypt. The initial install went smoothly, and I needed to enable the registry. I configured the registry following these instructions: https://docs.gitlab.com/ce/administration/container_registry.html#container-registry-domain-configuration, by uncommenting the registry_external_url line and setting it to my repo domain name - https://repo.thcguard.com I did not add a port because when I tried that previously docker login failed and I could never get it to work. I haven't done any other configuration on this instance.

The CI build process is working perfectly until it gets to the docker push command, then it fails with a 404 error shown below, which I truncated for brevity. The return is an html 404 page from gitlab. I get exactly the same results from my local machine running docker push manually.

$ docker push "$CI_REGISTRY_IMAGE" The push refers to repository [repo.thcguard.com/thcg/debug] ed1b7d66b02e: Preparing ced9a4d5e514: Preparing 6832b1e90527: Preparing 3eab067afe07: Preparing b14b059b334d: Preparing 1a9567e1252c: Preparing 6a00619a7f60: Preparing 12dc82ecd022: Preparing a09b2a536b3c: Preparing 22f6f380bfb5: Preparing 6227ccc48aa1: Preparing 0c0cd3677ec9: Preparing 8c0b45627f02: Preparing aef56da2eab2: Preparing 06cca0498901: Preparing 03901b4a2ea8: Preparing 1a9567e1252c: Waiting 6a00619a7f60: Waiting 12dc82ecd022: Waiting a09b2a536b3c: Waiting 22f6f380bfb5: Waiting 6227ccc48aa1: Waiting 0c0cd3677ec9: Waiting 8c0b45627f02: Waiting aef56da2eab2: Waiting 06cca0498901: Waiting 03901b4a2ea8: Waiting error parsing HTTP 404 response body: invalid character '<' looking for beginning of value: