On dashboards, when adding a new Performance Analytics widget to a dashboard's tab, the widget picker will get stuck loading content.
The root cause of this issue is due to having a special character on the Name, Lookup Name and Description fields of a Performance Analytics widget.
This usually happens when one of this fields were populated with a text that was copied from a PPT or Word document, or other modern text editors.
The "string" that gets copied contains special characters that are not rendered, therefore these special characters are not visible when generating the Performance Analytics widget record.
However the special character doesn't allow the platform to properly query and capture all the widgets to show in the widget picker, causing it to be stuck while loading it's content.
The Names, Lookup Names and Descriptions of the widgets that were copied and pasted from an outside resource such as a PPT or Word need to be erased and manually inputed. Update the record after modifying the fields to fix the record which will allow the platform to display in the widget pciker.