Visit my.sonatype.com for documentation on Nexus Repository version 2.
You've restricted read access to a repository by using a repository target with a regular expression that matches a group ID, such as "/com/mycompany/team-a/.*". This works, but now users with this privilege can't use the "Browse Storage" tab in the UI.
This is happening because the folders "/", "/com/", etc. do not match your regular expressions.
To fix this you also need to grant read access to the paths in the tree, so use a regular expression like this one:
Alternatively, you can grant access to all directory listings regardless of where they are in the hierarchy:
This will grant access to all directory listings, but will not grant any access to artifacts within a directory.