I guess you will also have to look at Cache-Control header of the page and its values, this can help vercel to return the page directly from edge network only, you might have values public, immutable, and may be the reason for revalidation not working.

I'm not 100% sure but once try changing revalidation time to 2 minutes and Cache-Control headers to never cache anything and try. also can read more here - https://vercel.com/docs/edge-network/caching