Is Vercel caching on top of Next.js cache management?

A little bit of context: I'm building an app linked to a headless CMS. To cache data, I use the unstable_cache function from Next.js. I also created an API route to invalidate the cache for a specific tag using the revalidateTag function from Next.js. It seems to work well. I can update my data in my CMS, and until I call the revalidating route, the data doesn't change. But when I call it, the data is updated. So far, so good.

However, lately, when pushing to production on Vercel, this doesn't work anymore, and I can't invalidate my data. Any explanation? Is it possible that the unstable_cache function is too unstable? is Vercel caching on top of my nextjs caching managment? is ther a setting I missed somewhere ?

Also, only the Vercel Purge cache button seems to resolve the issue