Netlify CMS config.yml errors

I have a two year old Gatsby site running on Netlify.
It uses the Netlify CMS.
The repo for this was on GitLab.

Recently I updated to Gatsby4 and updated the packages used to the current versions.
I did this in a new repo on Github and switched the site to use the new repo.
I changed the Git Gateway Service on the Identity page to point at the new repo.

The site builds and deploys, but when I try to access the Netlify CMS using /admin/ I get the following error:

Error loading the CMS configuration
Config Errors:
Error: Failed to load config.yml (404)
Check your config.yml file.

The location of the file has not changed:

The only change I’ve made to the config.yml is to the branch since GitLab uses master as the primary branch and Github is using main.

name: git-gateway
branch: master

name: git-gateway
branch: main

How can I research this issue?

FWIW - It works fine using gatsby develop on my localhost. I interpret this to mean the problem is not with the structure of my yml, but has something to do with the Identity setup.

Hi @witcradg,

We’ve responded to your question in the helpdesk.