Upon opening the Widget editor to edit any widget or the page editors to edit any pages, we would see the Authentication window keeps popping up again and again.
Any Release / Version.
This could be happening because of the missing Angular Providers on the instance (Either deleted or Missed by some other chances).
Download and Import the files Angular Providers to the impacted instance.
Also, go to the header menu widget and change the below code on the Body HTML template,
In the HTML Template of the Header Menu widget (as we have imported the menuTemplateEditor widget (one of the files in the attachment)).