Hello @FredericS, thanks a lot for taking the time to participate in the community.
In order to harder our images and follow best practices, we re now restricting permissions and following a model that is well described in this openshift document (please take a look at support arbitrary UserIds)
You can then use any UID and make sure GroupId is assigned to root.
Please let us know if you need more detail.
Cheers,
Jeremy.