Hi @crwntec, welcome to the Vercel Community!

I see that you see the item twice on the screen. Now the function you are referring to won't lose the processedItems Map because it is scoped within the function call. So, each function invocation will lead to a new map being created independent of others.

Coming to the file itself, I see two caches declared up top:

1// Add caching for IRIS data with a short TTL (e.g., 30 seconds)2const IRIS_CACHE = new Map();3const IRIS_CACHE_TTL = 30000; // 30 seconds45// Add caching for all API responses, not just IRIS6const API_CACHE = new Map();7const API_CACHE_TTL = 30000; // 30 seconds

Now, these Maps will be reused or not depending on if the serverless function is hot or reusing the same instance, which might be the root cause. I would say, try to debug your code assuming these Maps will or will not have the value cached. Maybe that changes the answer for you.

Generally, it is recommended to make your serverless functions stateless by using external data stores instead of relying on a global variable.

I hope this was helpful.

Hey, Firstly: Thank you for your feedback, but I have found the solution on my own. Even though your answer is not the cause of the problems, I think it might be a good idea to later switch to something like Redis for example!

In this case the problem was simple (and a bit stupid I guess). It turns out that running services that heavily depend on dates and schedules (like railways do in most cases) on a provider with a different timezone is not a good idea. After looking at the data I realized, due to Germany being GMT+1 my API was fetching data for the past hour and this caused the problems.

Sorry for bothering you as this is clearly not Vercel's fault.

Have a nice day crwntec

Hi @crwntec, oh that's insightful. Thanks for sharing your solution here.