An invalid filter has been left on the page, probably in the minion ID column, and the user has navigated away from the page.
Resolution
Right click on the spinning circle with your mouse
Select "Inspect" from the menu
This should automatically launch the developer tools in your browser bring you to the UI object
Hit the "delete" or "backspace" button on your keyboard to delete the spinning circle temporarily from the page
This should allow the already loaded portion of the page to become available
Click on the funnel icon for the column that has a filter and remove the filter
Alternatively, you can click the "Clear Filters" button to clear all filters
Additional Information
If removing the spinner does not activate the Filter or Clear Filter buttons, then the box behind the spinner needs to be removed. See this example from the Minion Keys > Accepted page: