Adding headers in server middleware doesn't work with Vercel cache

[ryanweston]

Hi, I'm currently trying to deploy server middleware that adjusts request & response headers for my routes. This works as expected locally, with the node-server preset and on my Cloudflare pages deployment.

However on Vercel none of the headers get proxied from the middleware as expected and the headers assigned on first run are cached with the route, resulting in sensitive information being leaked.

Can't get to the bottom of what's happening here. Any help or insight into the matter would be much appreciated.