Example below is shown for the default db prefix ‘wp_’.
1st, WordPress core stores user roles with capabilities at wp_options db table at option name ‘wp_user_roles’:
SELECT * FROM wp_options WHERE option_name='wp_user_roles';
If db prefix was changed, WP will not find its user roles.
2nd, look at the user-role-editor-pro/uninstall.php
You will see there where URE Pro stores its settings and additional modules data and how to delete theme using SQL tool.
It does not prevent access to the Users->User Role Editor menu. It seems you lost user roles, so try to change user roles option_name value using new db prefix.