CORS errors on back in stock form submission (started June 1st)

We use the “https://a.klaviyo.com/media/js/onsite/onsite.js” integration of Klaviyo. 

As of June 1st we get a CORS error when submitting the back in stock email subscription.

ERROR: Access to XMLHttpRequest at 'https://a.klaviyo.com/onsite/components/back-in-stock/subscribe' from origin 'https://www.yourSite.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Neither our code or config has changed, and this functionality has gone from working to broken.

Please advise on if there is any way for us to fix this our end.