Cannot save content, API returns "404 Not Found" for POST to /.netlify/git/github/git/blobs

[michael-gratton]

We are using Netlify CMS to allow people to edit content in a private, organisation-based GitHub repo. Netlify Identity is used to authenticate. CMS is configured with /edit/index.html and /edit/config.yml files per the Netlify CMS docs. Workflow mode is disabled.

This has been working fine for a while, but recently it stopped, and I can't figure out why. The CMS loads find after logging in, and content shows up as expected. However whenever clicking Publish Now after making some content changes, a POST to /.netlify/git/github/git/blobs is made, and the call returns a 404 NOT FOUND with the following content:

{
  "message": "Not Found",
  "documentation_url": "https://docs.github.com/rest/reference/git#create-a-blob"
}

NB per the GitHub docs referenced in the message above, the format for the equivalent GitHub API is /repos/{owner}/{repo}/git/blobs, so it seems like the CMS should actually be using a path like /.netlify/git/github/repos/OWNER/REPO/git/blobs - but I'm not sure why the actual POST's path is missing those extra path steps.

I have re-attached the GitHub repo to both the build and Identity several times over per other suggestions. I have also ensured that the Netlify and Netlify Identity GitHub applications have been approved, etc, etc.

Any suggestions about what else to check?