I was encountering a similar issue while using Portainer. I had pulled the image using the Docker command line but once I attempted to deploy the updated image Portainer threw the "access forbidden" error on the "/manifest" endpoint.

The solution was to add the registry to Portainer itself, rather than logging in through the Docker CLI.

See the Portainer instructions for adding a registry: https://docs.portainer.io/admin/registries/add