Hi, @zach, it sounds like the DNS change delays due to time to live values has already been excluded as the root cause.
My best guess as the most likely cause would be that site was at one point using a service worker.
We would also be happy to research the cause. To do this, we need to be able to identify which page loads are incorrect.
To this end, would you please send us an x-nf-request-id header for an incorrect response for any URL belonging to this site?
With that header, we can then find the exact request/response in our logging (and the logs are quite detailed). This will (or does in most cases) tell us where the issue is and point the way to a solution.
If there are questions or more information as well, please add them anytime. We look forward to finding out why this is happening and getting the issue resolved.