When you click the “Refresh” button under the grid in manager/?a=workspaces, it should make an AJAX-request with the action workspace/packages/getlist.
Can you open the developer tools in the browser, to see if that AJAX request works correctly (“Network” tab) or if there are any JS errors (“Console” tab).
The request to workspace/packages/getlist often takes quite some time to execute, as it queries the API for update information.
You could set the system setting auto_check_pkg_updates to No to speed things up.
Can you check the server error log, to see if a PHP error gets logged there?
What version of PHP are you currently using?