title: What is the "manifest blob unknown: blob unknown to registry" error
body: <p>I'm trying to push a multi-arch docker image to docker hub and run into errors (opened docker issue at <a href="https://github.com/docker/distribution/issues/3100" rel="nofollow noreferrer">https://github.com/docker/distribution/issues/3100</a>):</p>
  
  <pre><code>❯ docker build -t andig/evcc:latest-amd64 -f linux-amd64-.Dockerfile .
  ❯ docker build -t andig/evcc:latest-arm.v6 -f linux-arm-6.Dockerfile .
  ❯ docker push andig/evcc:latest-amd64
  ❯ docker push andig/evcc:latest-arm.v6
  ❯ docker manifest create --amend andig/evcc:latest andig/evcc:latest-amd64 andig/evcc:latest-arm.v6
  ❯ docker manifest annotate andig/evcc:latest andig/evcc:latest-amd64 --os=linux --arch=amd64
  ❯ docker manifest annotate andig/evcc:latest andig/evcc:latest-arm.v6 --os=linux --arch=arm --variant=v6
  ❯ docker manifest push andig/evcc:latest
  
  failed to put manifest docker.io/andig/evcc:latest: errors:
  manifest blob unknown: blob unknown to registry
  manifest blob unknown: blob unknown to registry
  manifest blob unknown: blob unknown to registry
  manifest blob unknown: blob unknown to registry
  manifest blob unknown: blob unknown to registry
  </code></pre>
  
  <p>Searching around shows error might be related to "foreign layers" (<a href="https://issues.sonatype.org/browse/NEXUS-11865" rel="nofollow noreferrer">https://issues.sonatype.org/browse/NEXUS-11865</a>) but it's unclear how that might happen building an image based on Alpine.</p>
  
  <p>As the docker github ticket and a forum question didn't get any response- what else could I do for further analysis? E.g., how could I find out which layer it's complaining about?</p>