Gatsby SSR - function SSR deployed but page is not found (404)

I’m still getting an 404 not found when trying to access my SSR page. In development (gatsby dev) all is working perfectly, but on the deploy-preview or even with local netlify serve that page returns 404.

The SSR function is successfully built and deployed.
SSR Page:

Furthermore, gatsby API handlers also stopped working (returns 404):
But when calling them from .netlify/functions it returns the right response