Selective failure pulling container from acr

Question

After a machine reboot on a cloud provider that is not Azure, I have a problem pulling the images.
Details:
Kubernetes 1.19.4
Image required through helm, with a secret docker-registry containing:
docker-email
docker-username
docker-server
docker-password
Error:
Mar 29 17:41:53 cluster-host1 dockerd[xxx]: time="2021-03-29T17:41:53.nnn+02:00" level=info msg="Attempting next endpoint for pull after error: Get https://ourcr.azurecr.io/v2/ourrepo/manifests/latest: unauthorized: authentication required, visit https://aka.ms/acr/authorization for more information."
Mar 29 17:41:53 cluster-host dockerd[xxx]: time="2021-03-29T17:41:53.nnn+02:00" level=error msg="Handler for POST /v1.40/images/create returned error: Get https://ourcr.azurecr.io/v2/ourrepo/manifests/latest: unauthorized: authentication required, visit https://aka.ms/acr/authorization for more information."

I have tried various actions, including logging with the same user and password from my dev machine on az acr (success), perform a
docker login
on the cluster-host1 (success)

The puzzling thing is that another image pull few seconds apart for another container from the same cluster succeeds!
I fail to understand what is the difference.
We are using access keys with the password directly, and it has been working for months now.
Thanks for any hint. Hubert J.