Docker Hub cache not working - Unkown blob error

Hi,
I am trying the setup nexus as a docker cache.
having got it to work with ssl/https the repo populates with the requested pulls but the client fails with an unknown blob error!
[root@ci-test-vm ~]# docker pull alpine
Using default tag: latest
Trying to pull repository docker.io/library/alpine
sha256:69e70a79f2d41ab5d637de98c1e0b055206ba40a8145e7bddb55ccc04e13cf8f: Pulling from docker.io/library/alpine
540db60ca938: Pulling fs layer
error pulling image configuration: unknown blob
the repo is populuating the images
Index of /v2/library
Name Last Modified Size Description
Parent Directory
alpine
ubuntu
How do I fix this??