Tanstack Start Server functions cookie issue

Hi, I'm having trouble getting session_data cache cookie to update when I use the auth api inside a tanstack start Server function. It is similar to next.js I think, and I have recreated a version of the nextCookies() plugin for tanstack start. problem is it works perfectly in development server, but not in vercel/netlify deployment.
can anyone confirm if they have the same issue or help? thanks!