appengine randomly serves old files

I'm currently using Google Appengine to host a website with Golang as the backend. I have a custom domain setup and (sometimes) it works perfectly fine. My website requires some css and js files from the server. These were served perfectly in the past but now it randomly stops working. Both on the "mydomain.de" and on the "myapp.appspot.com" domains. Sometimes it works on the normal domain and then it works on the other and sometimes even on both. But if I reload the site after a couple of minutes it just shows me an old index.html file (that I have removed days ago).

Did someone experience this problem in the past and does anyone know a fix for this?

Thanks in advance.

Have you ruled out your browser cache as the source of the problem? If after getting a stale version, shift-reload (assuming Chrome or Firefox) brings up the desired version, then look into how to do "cache busting" for css and js, and check the app.yaml doc for how to set expiration times on static assets (assuming your index.html is static).