Error "Uh oh Something went wrong" when adding users to site-admin group

Summary

The error "Uh oh Something went wrong" is being thrown when adding users to site-admin group on the new user management view. However, the user is added to the group.

Environment

New user management view.

Steps to reproduce

1. Go to user management;
2. Add a user to the site-admin group;
   1. Groups > Site-admin > Add member;
   2. User profile page > add group > site-admin;
   3. Users page > three dots icon > add user to group.

Expected results

A success message should be shown.

Actual result

The error "Uh oh Something went wrong" is shown. However, the user is added to the group.

Workaround

Refresh the page and the user will be added to the group.