There could be multiple explanations, it's not possible to answer your question without additional information.

Here is usual cases:

1. Your users don't have appropriate ROLE assigned to them.
2. Somebody change permissions in repository for a role on some level, usually it's permissions for "ROLE_USER"
3. Somebody renamed "ROLE_USER" to something else
4. Some sub-resources are not allowed to be read.

etc ...