From Version 5.6, users no longer listed in the Effective Permissions tab if they grant the permissions to the repo by membership in a group (and not directly for the user).
To reproduce (on 5.6 and above):
1. Create a user and a group
2. Assign the user to the group
3. Create a permission target and give the group some permissions
4. Click on the repo in "Artifact Repository Browser" and go to the "Effective Permissions" tab
Under "Users", you will not see the created user, but only its group under "Groups".
This is a regression since before 5.6 (access) it works differently, users are listed in this section even if their permissions is only via their group