Repeating DUO screen on endless loop after approving on phone.

In a Drupal 7 multisite instance, we have this module working on about 8 sites. However, on one site in particular, the DUO screen reloads after a confirming on my phone. After confirming, I see green text saying that it was approved. However, a new DUO UI loads again. On investigating more, I'm seeing the following message in the browser console.

Content Security Policy: The page’s settings blocked the loading of a resource at self (“default-src https://api-123ab456.duosecurity.com”).

If left, this will keep repeating in an endless loop.