Relationship Field Not Working Anymore

Hi,

I created two CPT's in MetaBox. One is doctor and the other is room. The idea is to choose the doctor that works in a specific room as the rooms are not used by one doctor only.

I also had created custom user roles and one such role is called Assistant.

Up until couple days ago I think, for more than a year, this setup worked perfectly. But today the users told me that they cannot select the doctors when editing a room.

I tried it with my admin user, no problems. But when I logged in with a test user (assistant role), I see that they the list shows no doctors at all.

There's been no changes in the site, settings, etc. All of a sudden, the relationship field to choose the doctor within the Room CPT doesn't show any doctors for the user roles.

Capability type for both CPTs is post

Here's a screenshot of the CPT settings:

Here's a screenshot of the Relationship settings:

Here's the code snippet example I used to add the user role assistant.

add_role('assistant', __(
   'Assistant'),
   array(
       'read'            => true, // Allows a user to read
       'create_posts'      => false, // Allows user to create new posts
       'edit_posts'        => false, // Allows user to edit their own posts
       'edit_others_posts' => false, // Allows user to edit others posts too
       'publish_posts' => false, // Allows the user to publish posts
       'manage_categories' => false, // Allows user to manage post categories
       )
);

Kindly asking for ideas. Thank you all and the team.