This can occur when the docker registry config isn’t quite correct, so it’s checks for whether an image exists always return False. I recently hit this myself when I was updating ovh.mybinder.org. We had the config:
when what we needed was:
/binder on the registry url in that case). The result was that the images it looked for had an extra
binder/ on the front, which weren’t the ones being pushed.
Check the logs of BinderHub, possibly with debug logging enabled:
You might see something useful that hints at why it’s not finding the images.