This user provider_namespace does not have an associated namespace https://galaxy.ansible.com/api/v1/provider_namespaces/11551/

There for the v1/roles api will 500 when this shows up in the paginated list, at the moment it occurs on this page (but it may occur in a nearby page): https://galaxy.ansible.com/api/v1/roles/?page=265

This user should get a namespace (existing or new) associated with it.